Old High end Receivers VS New Low end

I don't believe amp technology has improved significantly in recent years, however it seems to me that you can now buy a full featured and powerful receiver for cheaper than you used to be able to (considering inflation, not necessarily list price.)

As for sound, well...that strikes me as rather subjective.

Some people feel that you should buy a reasonable quality receiver with the features you want, and then back it with an outboard amp. That way you get the best of both worlds - an affordable pre processor (you can't beat mass market electronics for cost,) and the amp of your choice (with all the power you can afford.)

You say power isn't important. But sound quality clearly drops as you push the amp towards it's limits. Anecdotal evidence suggests that power is an important part of amp sound quality for that reason.

Or you could keep the Sunfire and feed the outputs of the new receiver into the inputs of the Sunfire keeping all the good amp qualities and upgrading the processing with new features. Or keep the sunfire and get one of the new Onkyo/Integra pre pros and hook it to the Sunfire for amplification.