I have never written a very in depth review before, especially not on this size platform. So please Bear with me, pun intended. Anyway let's get started.
I have been using this combination for a few days now and the products just moved me to write this review so I hope someone else will find it interesting/helpful if your looking into either device.
Let's start with the Hifiman cans. I will break them down into sections: Build quality, Value, Staging, Highs, Mids, Lows, and overall sound.
Build Quality: 9/10
These are great in this area, the only reason I docked a point we're the fact they did use plastic in a couple places the housings them self are plasic, but feel sturdy. As well as the adjustment slide housings are also plastic, but again I don't think they are gonna break. One other thing that's plastic is the ring on the back that holds the mesh liner in behind the drivers. But again no harm no foul. I have dropped these unfortunately a couple times with literally no damage. The focus pads do great for me personally, the head band is great and comfortable. The only thing I think somepoeple may change on these is the cable which for me using portable the 90° jack works fine but others will have other uses. All in all great build, comfort, and design.
Value, value, value. A planar with this build, with this sound, at this price point? I shouldn't need to say more. Would be hard pressed to find much that beat it for the price. If you could. Lesser models have much worse build. They really went all out for the budget.
Sound stage: 9/10
These things sound staaaaaggggggeeeeee is that wide. Goes for days it really separates instruments and different notes in songs remarkably. Everything seems to have it's own place somewhere around you in the song and they are very accurate. I often find myself listening to a EDM track and focusing on one sound just waiting for it to come back and you can literally single out every instrument with these absolutely great detail, separation on these.
The highs on these are actually the best part about these. The highs are very much so present. They demand your attention without being overbearing. They are never distorted while powered properly. And never recessed to the point when you may miss something in the detail. Don't be worried about sibilance or being to harsh. Even while amping these at moderate volumes I personally do not find these to be harsh in fact I find them to be just about where they should be.
Now wait just because I docked two points does not mean the mids are not good on these cans, because they are. I only gave an 8 due to the face in treble heavy songs I have found that the mids just don't sound as present. I'm not sure if it's the producers preference of the song, or just me. I really think the main reason is the highs are so good I find myself zoning in on what's going on up top and not paying as much attention to what's sandwiched in the middle. I admit these are a pure joy to listen to. And that is my opinion yours will likely vary. Don't let this 8/10 fool you they don't lack.
Now here is a controversial spot. I'm a bassheads at heart. Who isn't? Everyone can enjoy that heart throbbing ear rattle. BUT. And that's a big but. These do deliver at times on certain tracks just that. However these are a fairly neautral can. The signature isn't V shaped or one sided. That being said with everything else that's going on just how much bass they are putting out can be deceiving as well as the fact that these are open if the environment is noisy that also takes alot away from the bass section. The bass is very present, accurate, and appropriate. I love the way that they worked the bass in with these. It's never muddy, bleeding into the mids, just where it should be for a non mainstream can. These are audiophile tuned so if your looking for something that sounds bass boosted all the time and distorted and muddy these aren't for you. (If you like beats, go away).
Overall sound: 9/10
The sound on these all blended together is a eargasm. It is literally quite dreamy I have listened to any genre through these you can think of. And everything sounds wonderful. The damn things are just accurate and fun to listen to. Absolute joy to listen to. I find myself not wanting to take them off.
To close with the cans, at this price point if you buy them and don't like them or happy with your purchase I think your just hard to please. For the price these are magnificent. I mean they are just down right great. Comfortable, durable, sounds is great, cheap. Can't go wrong. Biggest downside for me was the driving of these. They aren't the most efficient. Alot of people have said drive them off your phone they work fine. But in my experience using my Pixel XL they work but are way to quite not enough output from my phone. I think most phones won't push them properly you will want a amp. Which if your serious enough about audio isn't an issue. That is literally the only complaint I have had with these at all. I would recommend these to anyone buy them for a budget can they are worth every penny they are asking, get them while you can!
Now on to the Little Bear B4. I will break them down into Value, Sound, Build, and battery life.
Really a great amp, you can get more power for cheaper. However the competition isn't portable tube amps that's the niche these have. These have that going for them.
Sound is great, clean power, doesn't add distortion even at high volume. Does it job and does it well. I find it to be a tad neutral compared to other amps I've used. Some say it's a little warm and I could see maybe a boost in the mids which is what the 4XX needed more than anything so these are a perfect combo.
Build is literally where this shines. Mostly made of metal. Metal heatsink, metal volume know that has no play in it. I have not taking heatsink apart but the window you can see through displays a few components. And it's encouraging to see they did use nice American made Raytheon tubes. Build is excellent with this.
Battery life: 9/10
I have used this thing full tilt for about 5 hours. And it still had some power left. No light indicator to tell how much power is left which is a downside. All in all I have seen reports of people claiming 10 hours and I could believe that.
Overall the little bear would be a great option for portable use with most any cans I think and I believe most anybody will find the purchase to be a good investment.
Both are great products that I highly recommend and great values. And a great pair together.