You could integrate your 2-channel with your H/T, but it would be a real bother IMO. There have been some amazing threads and suggestions recently regarding H/T. Personally, I say keep them seperate if at all possible.

I have recently purchased a tube amp. Tube amps are partial to horn style speakers. Perhaps you are familiar with the brand Klipsch? I use that as an example of a horn loaded speaker. Also, a full range, high efficiency speaker would do well with a tube amp. Tekton is a good example of this.

Here is a Klipsch RB-61 horn loaded speaker,



Here is a Tekton Model 6.1,




Both of these retail around $400 USD new. A nice used option would be this guy on Ebay. He builds a nice full range DIY speaker and puts them up for auction. Check it out...http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT



As far as the amp goes, for under $500, you'd be looking at high quality used. As noob said, check Audiogon. If you look on Ebay, you can find hobbyists who convert the old console tube players into small, efficient tube amps. They usually sell them quite cheap.
Hope this gets you going...