[sonci]

Since you are a Rush fan I`m posting my opinions as well,
I wouldn`t worry of Kmixer, unless you are using XP,
Using directsound has its advantages, such as not messing with ASIO drivers which smt can be a pain in the ass.. as you said there`s no big difference after all, the same as comparing Flac with v0, we know flac is better, but not always we can distinguish them,
also if you have a bright sounding system, directsound can help a bit in "warming", Asio usually is too analitical, while wasapi, well I dont use it unless written on soundcard box "wasapi compatibel"..
 
The Omega card should be fine, (though never tested it), in fact I dont think there`s much difference between soundcards at that price levels, but in HeadFi 80% of recommendations go for an Asus card, the rest for Creative, and Audioengine monitors, just marketing.. 

 

[TitaniumDust]

I'll give you my opinion on this matter, but remember I do tend to have "golden ears" (which partially explains my account here at head-fi).
 
Bottom Line:  What I would do is use foobar (or another player player that supports both methods) and see if you hear any difference between DirectSound and WASAPI.  If you hear very little to no difference, I'd feel pretty confident that the choice of player won't matter to you.
 
I, personally, hear a difference between DirectSound and WASAPI and ASIO, and the difference ain't minor.  They all sound different to me.  DirectSound sounds like I put some foam in my ears and then put on my headphones.  WASAPI sounds better - better imaging and soundstage, but still somewhat fuzzy and out of focus.  ASIO sounds the best - more focused imaging and more clearer/open soundstage, with the slight fuzziness removed.
 
I also recently did a comparison between foobar and J. River and was astonished to find that J. River sounded better as I A-Bed it.  If you are not altering the sound at all, no volume control or DSP (aka BitPerfect), the difference was quite minor but still noticeable to me.  If you hear no difference between DS and WASAPI as above, you probably wouldn't notice this difference either.  As soon as you do any kind of volume control / replaygain or DSP/EQ, though, J. River took foobar to school.  I know its blasphemy, but I use replaygain (J. River calls it volume levelling, I think) and I also use a professional 64 bit VST parametric EQ.  J. River's audio path is purely 64 bit which probably accounts for the difference in SQ I hear.
 
Remember, this is just my own opinion as heard by my ears and using my equipment.  Your experience may vary.

 

[vantagesc]

  also if you have a bright sounding system, directsound can help a bit in "warming", Asio usually is too analitical, while wasapi, well I dont use it unless written on soundcard box "wasapi compatibel"..

 
Started thinking why my Shure SE846 sounded more relaxed and somewhat veiled while listening through my PC vs. iPhone (both through my JDS C5D AMP/DAC).  Noticed my iTunes was set to directsound and after switching to windows output session, I agree with you.  Very noticeable difference.  I could see someone preferring directsound with a more analytical sounding phone, e.g. Phonak PFE w/ grey filters.