If I'm looking at the current ongoing drops correctly for the O2 and this DAC, one of the reasons you would want to get the separate pieces over the O2+DAC revB combos (JDS Labs and Mayflower) would be the dedicated RCA output on these, correct?

More to the point... as far as I can tell the two outputs are NOT separately buffered (and I'd be surprised if they were). There are not two separate analog output stages, they are paralleled and share the same output stage. What's that mean? If you connect two amps that have 20k ohm input impedances, the ODAC output stage will effectively "see" an amp of 10k ohm. If they only have a 10k input impedance, the ODAC will "see" 5k. As the amps' input impedance goes down, the question at some point becomes can the ODAC deliver the necessary current to properly drive those two amps? Not sure at what point that is, but keep in mind that the ODAC is deriving all of its power from USB bus power that may only be capable of 5v at only 500mA. But as the high1 said, most amp input impedances SHOULD be quite high.

I think I read somewhere that the ODAC was designed to output to devices with at least 10k input impedance. I imagine that this is the optimal recommended value, and that you can still get it to work with lower resistances, albeit with less predictable outcome.

So if I plugged in two different amps (one to the 3.5mm output, the other to the RCA output) simultaneously, the line out would be lower in volume in each of the amps compared to if I just used one output at a time?
This is all new to me so I would like to know as much as possible. Having an idea of how the outputs work when plugged in simultaneously will affect my gain options for the corresponding O2 amp drop if options are offered.

yes, I can't say exactly same.
maybe little bit lower, but not much
Beacuse input impedance are quite high(Headphones are 16~600ohm, Speakers are 4~8, Amps are 10k~)
simple you can imagine the results by neat formula V=IR, 1/R¹+1/R²=1/R
ex)100k,10k you can get 9k ohm
(Of cours Vrms has related with more factors, but anyway we talk about flow, and simple ver.)
and I recommend set the one of your gain at x1(no resistors)
Some reference for you : iPhone, iPod touch 1Vrms, iPad 1.5Vrms
in my case, even K701 doesn't need full volume of iPod touch(direct)

probably. lol
but, I just wanna be helpful to others.
if you feel uncomfortable with my replies, tell me why and point them to me.
I'll try to correct them!

Thanks for the heads up, my set up is probably going to be ODAC to a O2 and a Little Dot MKIII. Ideally, I would like both amps plugged in at once. The reason why I might stick with 2.5x/6.5x gain is because I'll be using high impedence headphones like Beyerdynamic DT880 (600 ohms) and Sennheiser HD650 (300 ohms).

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maybe almost 2Vrms each

This is all new to me so I would like to know as much as possible. Having an idea of how the outputs work when plugged in simultaneously will affect my gain options for the corresponding O2 amp drop if options are offered.

simple you can imagine the results by neat formula V=IR, 1/R¹+1/R²=1/R ex)100k,10k you can get 9k ohm

(Of cours Vrms has related with more factors, but anyway we talk about flow, and simple ver.)

and I recommend set the one of your gain at x1(no resistors)

Some reference for you : iPhone, iPod touch 1Vrms, iPad 1.5Vrms in my case, even K701 doesn't need full volume of iPod touch(direct)

but, I just wanna be helpful to others. if you feel uncomfortable with my replies, tell me why and point them to me. I'll try to correct them!

http://nwavguy.blogspot.kr/2011/09/all-about-gain.html

http://nwavguy.blogspot.jp/2011/09/more-power.html

(at that time iPod touch has 0.5Vrms, half of iPod touch 5 = 1Vrms)

O2 has dual gain, so I recommend x1 and another(x2, x2.5, x4, x6, x6.5 what ever you want)

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