I purchased the Musiland Monitor 01 US from a USA re-seller on Ebay for around $80 shipped.  I have used the 01 US now for about a month and I thought that I would provide a brief review for those of you who are curious about a reasonable USB DAC that handles up to 24/192 audio.
 
The 01 US is a small portable DAC that is housed in an attractive curved gray metal enclosure with quality connectors.  A single USB connector serves as the input while standard RCA analog phono jacks, a 1/8" stereo headphone mini-jack and an optical TOSLINK connector are the output options.  The unit is powered by the PC via the USB connection.
 
The 01 US headphone output is controlled by your PC and player client (I am using Foobar 2000).  The output has adequate power to drive my Beyer DT880s, although I prefer using the RCA high-level outputs to drive my various headphone amps.  Most of my source library material consists of 44.1 FLAC files with some hi-res 24/96 and 24/192 FLAC files obtained from various HD music sites.
 
I have spent quite a bit of time listening with the DT880s and with my slightly modified JVC HA-RX700s (I tweak the high freq response of the RX7000s using Foobar's equalizer). 
 
In short, this little gem delivers.  With 44.1 FLAC files, the 01 US presents a huge soundstage with excellent depth.  Imaging is rock-solid and individual instruments are nicely separated.  Detail abounds and inner resolution is superb.  But, it's the hi-res FLAC files that are the icing on the cake here - they sound wonderful with lovely, shimmering highs and deep, deep lows - analog sounding actually - definitely a step beyond my Esound and Harman Kardon CD players and perhaps even my Clearaudio Emotion turntable.
 
The Musiland driver client is not very sophisticated, however, and in fact is sort of the weak link in the package - the software has crashed several times.  I would suggest keeping the SR Control setting on Auto in the Advance tab.  I played with that setting and it ended-up causing the driver to get out of sync with different res files - the result was dropouts and it took me awhile to realize that I needed to re-boot the unit and the driver software.  So, if you have a 01 US and the sound changes from perfect to well, not so perfect, re-boot the unit and the driver software (and possibly your client), before you start messing with anything else on your PC.  Also, the driver (and accompanying documentation) is somewhat cryptic as the Chinese to English implementation is not exactly 100% intuitive.
 
Nothing's perfect in this world - the driver software is clearly a work in progress, but the Musiland 01 US is a compelling and amazing bargain for $80.

I am an old time audiophile - I started off my headphone "career" back in 1971 with the original Sennheiser lightweight phones (white plastic with blue or yellow foam pads).  They were a revelation in the 1970s and as my interest in the hobby progressed, I purchased and enjoyed most of Sennheiser's popular models (except the HD 800 and HD650). 
 
But over the past 10 years or so, I drifted away from Sennheiser and I have mostly used Beyerdynamic or Audio Technica cans.  Recently, on a whim, I decided to buy a pair of "refurbished" HD 428s from DAKMART for just $23.98 and I must admit:   Sennheiser has come a long way with respect to a closed headphone design.
 
First, the HD 428s are quite comfortable.  Well, maybe even extremely comfortable as they are very light and the fit is excellent.  Next, these cans deliver solid, clean, extended bass - impressive bass, actually.  Colored?  Perhaps.  Well, yes a little.  And the upper mid bass suffers because of it, but the all important midrange is fine and the highs are very clean and nice, if not a tad recessed.  Detail and soundstaging are really impressive for closed phones. 
 
The negatives?  Very few, actually.  The construction quality is, well, "plastic-y", so these are not super rugged, but certainly they are fine enough for home use. 
 
The only real negative is the short, very thin cord.  That is small print that comes with the bargain.  The refurbished model I received is the HD 428 "S" version which comes with an extremely thin, 4-foot long cord.  It does also come with a 1/4" adapter, a plus for sure, but the cord is silly thin and short - oddly out of place for the excellent sound quality the HD 428 delivers.  But don't let the cord scare you off.
 
In short, the HD 428 delivers in spades and these phones are, without question, a gateway to true high end sound for very, very few dollars.  If you are on a budget or just starting out, consider starting here.  Pair these with a $50 Cmoy amp or an inexpensive Bravo or Indeed tube amp from China and you'll be pleasantly surprised what your $100 or so has returned in listening pleasure.   You may not need anything else.