I hate to be the bearer of bad tidings, but Thiel speakers are probably the last speaker you would want to use with a budget receiver. They have complex crossovers that suck enormous amounts of power, and they are very revealing and will thus show you any weaknesses in the rest of your system -- in short, they have to be run with a high-current, high quality amp and high quality associated components to sound right. You've been lucky that your Onkyo hasn't blown up -- you may not be so lucky if you try another receiver on them.
A solution would be a Bryston 3B-ST, which will run you $750 to $900 used. All Bryston products are very solidly made and come with a twenty-year transferrible warranty, which makes a used purchase pretty risk-free. Bryston makes multichannel amps as well, but even used, they will be out of your price range. Try to find some used Cardas Golden Cross interconnects and speaker cables for the rest of your system.
The other alternative is to sell your Thiels and buy speakers that are more appropriate to run with a receiver. No offense intended, but again, Thiels are very revealing speakers made for critical listening to stereo music, not for casual home theater systems. They will work in home theater systems, but must be run with very good amplification, source components and cabling, or they will sound like hell.
A solution would be a Bryston 3B-ST, which will run you $750 to $900 used. All Bryston products are very solidly made and come with a twenty-year transferrible warranty, which makes a used purchase pretty risk-free. Bryston makes multichannel amps as well, but even used, they will be out of your price range. Try to find some used Cardas Golden Cross interconnects and speaker cables for the rest of your system.
The other alternative is to sell your Thiels and buy speakers that are more appropriate to run with a receiver. No offense intended, but again, Thiels are very revealing speakers made for critical listening to stereo music, not for casual home theater systems. They will work in home theater systems, but must be run with very good amplification, source components and cabling, or they will sound like hell.