First off, some random thoughts:
Powered speakers are fine, but they limit your possibilites by having only one input. There are some fine integrated amps out there that will serve you quite well, particularly if you're sure you don't want FM as part of the deal. This will allow you to choose from a pletora of passive speakers which far outnumber the choices of powered speakers out there.
As for that ".1" channel, well it simply doesn't exist in a stereo world. that's a separate, discrete, channel in home theatre that carries only low frequency information for movie sound tracks.
You CAN, however, add a subwoofer to any system you come up with. This can always be done at the speaker level or, if your equipment allows, at some point before the power amp. This might be cumbersome to incorporate into a system using powered speakers.
Depending on the quality of the sound card in your computer, you may (or may not) gain some performance by using either a different sound card and/or a standalone DAC. That, I'll leave up to others to take up with you.
For that matter, there are stereo receivers and some integrated amps that have digital inputs built in, but that's not too common.
You would be wise to discuss your final choices before purchasing to be sure they play well together. After the purchase is a bit too late, as some have found out.