The main problem with computer speakers is the satellites and the subs are in different places. separated by a thick piece of wood or whatever your desk is made from. What this means is your satellites need to play as low as possible so that you can get a halfway decent mesh with the sub. the problem with that is that to get low, you're going to have pretty big speakers. My current project uses a 4.5" driver and still needs to use a 3-4L box. This is small in the loudspeaker world, but not when they're sitting on your desk. The other thing I would be concerned with is the crossovers. You don't want your satellites playing lower than they are designed for because you'll end up with a lot of distortion, especially if they are ported. I am not very familiar with the various active studio monitor offerings. I don't think thats the way you want to go if you're looking for hi-fi.
for multichannel here's what I'd suggest
For $300-600 you could get something like one of the 5-6 channel amps by rotel, parasound, harmon-kardon, adcom, carver, etc.
Add one of the popular 5pc HT sets like Energy Loudspeakers Take 5.2 $3-600
For the sub you could do something like the sony SAWM40 for $150 dollars. SVS' are big and a lot more expensive. subs are too easy to DIY so my experience with commercial stuff is pretty limited. REL has been the only commercial brand that has impressed me, but they are really pricey.
If you just want 2.1, you can get a little more extravagent, but you have to be careful. Most of the systems are going to be designed with a seating distance of 6+ feet in mind. Be sure to go to all the local hi-fi shops and ask to hear the stuff you're interested in up close. I would tell you to try the magnepan MMG's, but I think it would be a nightmare getting them in a position that sounds good near your computer. There are so many systems that all sound good in the $500-$1000 range its impossible suggest something. some brands off the top of my head to check out though.... B&W DM 602/603, JMLab Cobalt, Dynaudio Audience Series, ProAc Tablette, Snell, Tannoy, etc.
Can't help you with 2 channel amps/integrateds. I haven't really listened to anything in the "mid-fi" range. seems like its always somebody's junk sony receiver or a Krell/Levinson/Pass. no middle ground...except for the amps I have built myself.
so what is my purpose for this post? Its an endorsement for do it yourself audio! It wont be much cheaper, but it can be a lot better if you have the time.
jt