Are you absolutely sure that its the amp? A channel can go out on a preamp also. To test it, just swap the IC's on the back of the amp. (l to r, r to l). If the right channel goes out after you swap the cables, its something else other than the amp.
Regardless, I don't think the i300 will be an improvement. If you want to try Krell, look for a good used KAV-250a. I've seen several of them come up here recently well within your price range. It would be a huge step up from the Aragon. That said, if your amp is working OK and has suficient power to drive your speakers, a new preamp should give a bigger improvement in sound quality.
Regardless, I don't think the i300 will be an improvement. If you want to try Krell, look for a good used KAV-250a. I've seen several of them come up here recently well within your price range. It would be a huge step up from the Aragon. That said, if your amp is working OK and has suficient power to drive your speakers, a new preamp should give a bigger improvement in sound quality.