Looking for the best 2.0 speakers (around 500-600$ max)

For music and for the same $$ you would definitely see SQ in a good 2.0/2.1 >>> any 5.1s because those 5.1 cheap out with horrible satellites with awful driver/tweeter design (or no tweeters!) Also allocating only up to $250 for speakers but $230 for sound card/DAC is just not good use of $$ for best SQ your money can buy... 

5.1 only works well if you have a big enough room and can place the speakers properly otherwise forget about it a 2.1 would be better, always use the rear jack, the front jacks internal wiring has to run the lengh of the noisey pc case full of RFI so picks up about 10times more noise than a rear jack.

Audioengine A2 is fantastic for the price. I've never heard the Promedia so don't take my word on this, but just from looking at it and reading the description I have a feeling it's probably not as good as the A2. The plasticy housings and "THX Certification" just screams cheesy computer speakers to me. Again that's just speculation. 

As for lossless FLAC 16/44 vs 24/92 or 192 etc, this might depend on your own ears, but for me I think there is a big difference. Not total night and day, but significant. If I hear the same song in high resolution and then go back to redbook 16/44 it feels like there is something missing. I can tell the difference on the A2 for example, if you were wondering.

Both the Asus Xonar Essence STX and Creative Labs Titanium HD will not do Analog 5.1 speaker setup, only Analog 2.1.

They will do Digital 5.1 speaker, but only with the more expensive 5.1 speakers with a Digital input (optical or coaxial).

Creative Labs is coming out really soon with two more sound cards (Soundcore 3D), prices unknown.

I like the Klipsch ProMedia 2.1 because the desktop speakers are small.

Price is around $80-$100 for used (eBay), where I bought mine.

A2 > PM 2.1 (current gen) for clarity and details in the treble and high mids, PM 2.1 (current gen) > A2 for everything else and high volume (75% of maximum) listening of music and movies. The A2 simply does not scale well when you give it more juice. The PM 2.1 horn tweeter depends on the enclosure for dispersion which leads to a wider soundstage than what the A2 can deliver. As a result, the PM 2.1 has greater potential as a very near-field system. However, the soft dome of the A2 sounds more accurate when properly oriented. The two sound absolutely different with the A2 being more mid-forward and the PM 2.1 much more laid back. If you can find an older set of the PM 2.1 with the original 17 lb. sub, jump on them. The current PM 2.1 revision is inferior in every way (build quality, SQ) to the original release (I had two sets of the originals, two sets of the current revision). Offhand, I feel PM 2.1 (previous gen) > A2 in general and across all genres of multimedia. A2 sub out is somewhat useless without a shelving filter to help clarify the mids by reducing the double bass effect. However, A2 + sub w/ high-pass filter enabled > PM 2.1 (any revision) except for high volume listening (parties, watching movies at a distance from the computer). 

Quote:

Originally Posted by adamlau 

A2 > PM 2.1 (current gen) for clarity and details in the mids and highs, PM 2.1 (current gen) > A2 for high volume listening of music and movies. The A2 simply does not scale well when you give it more juice. The PM 2.1 horn tweeter depends on the enclosure for dispersion which leads to a wider soundstage than what the A2 can deliver. However, the soft dome of the A2 sounds more accurate when properly oriented. The two sound absolutely different with the A2 being more mid-forward and the PM 2.1 much more laid back. If you can find an older set of the PM 2.1 with the heavy sub, jump on them. The current PM 2.1 revision is inferior in every way (build quality, SQ) to the original release (I had two sets of the originals, two sets of the current revision). Offhand, I feel PM 2.1 (previous gen) > A2 in general and across all genres of multimedia. A2 sub out is somewhat useless without a shelving filter to help clarify the mids by reducing the double bass effect. However, A2 + sub w/ high-pass filter enabled > PM 2.1 (any revision) except for high volume listening (parties, watching movies at a distance from the computer). 

Interesting thoughts. Being in a smallish size bedroom, I haven't felt the need to turn my A2 up all that loud, and so feel that they have an adequate amount of power/volume. Then again I'm not sure just what you mean by "high volume listening." Not that I listen at very low volumes, but I don't blast my music when I listen either. The lack of a subwoofer with the A2 could still be an issue for OP if that's a priority however. Given the limitations of such a setup, I find the bass is enough for music (though honestly I listen with headphones more often as of late), but a sub would definitely be nice for movies and gaming.

Paradigm is also coming out with a new set of powered speakers, confusingly also called A2. Although I think that's meant to be A squared, stands for Active Atom. That could be interesting. I wonder how it would compare to the Audioengines and the PM 2.1.

I thought the a2's sounded like mud, frequency responce graphs confirm this as the 200hz-100hz range plays +10db louder than the rest of the frequency range you would really need to eq them, and they are ridiculously over priced you get very little for your money in terms of sound quality, look at the range of edifier monitors the r1600t , r1900 , r2000 there much better and much cheaper they sound like speakers that cost twice as much so there good value for money.

Agreed regarding A2 muddiness. The issue with most miniature multimedia speakers is the hollow middle, of which Audioengine clearly opted to address by compensating the midrange forward. The issue is that when any amount of bass is introduced into the playback stream, the mids start getting lost as there is only so much a 2.75 woofer can do. Turn up the volume and the situation only worsens with creeping distortion.

The promedias are 2.1 with a 6.5" sub, the samsons are based on there studio monitors, the samsons sound have better sound quality but no where near the bass of the promedias, these are simlar to the samsons  http://www.amazon.com/Alesis-M1-Active-520-Powered/dp/B000EJTXZU/ref=sr_1_1?ie=UTF8&qid=1319645755&sr=8-1 theres also a usb version http://www.amazon.com/Alesis-M1Active-520-USB-Nearfield/dp/B001T9O5UM/ref=pd_cp_MI_1 , there about $10 more than the samsons 4i.