StandUpI am...
Also I think people should download and listen to the 10hz - 200hz test from here: http://www.audiocheck.net/soundtests_headphones.php ... I can understand why people think these don't have any bass, however I feel their impressions might be affected by the typical consumer sound signature which is emphasized bass and treble. These are very flat throughout their frequency. The bass goes deep and is present however it's not as prominent as a pair of Beats by Dre.
StandUpWith and without an amp (with both FLAC and MP3s), they have good bass for me. It isn't overpowering, but it is very clean and responsive to my ears. A good test for me is listening to Niels-Henning Ørsted Pedersen. The K553s keep up with the pace of his playing very well. Notes are distinct with good timbre.
When connected to my Samsung Galaxy Note 2, I find that the power drawn is similar to my Havi B3 Pro 1s. Normal listening levels are between 9-12 and loud is between 12-14 with 15 (max) being just consistently a little too loud for my ears. So they draw more power than conventional IEMs, but are quite usable with the Note 2--just not much overhead.
They do benefit from being amped (all I have in that vein is an Audioquest Dragonfly 1.2) but not hugely. I'd like to try them with a more powerful amp, but that will have to wait until funds permit which may be some time...
So far, I am VERY happy with them. I agree with some other commenters, though, that users of other headphones and IEMs that have an elevated bass might find these thin in comparison. That's why I recommend listening to them for several days exclusively to accustom your ears to their signature and then try doing a comparative test. If your other headphones/IEMs still sound better to you, then clearly your ears/listening preferences call for something with an elevated bass.