time to upgrade new receiver or used seperates?

I am long over due for an a/v set up upgrade. I have had an Onkyo tx-sv424 since it was new and dont even run pro-logic mode because it sounds horrible.I just got done building a nice set of diy speakers and now am looking to upgrade my receiver. I have been looking at the Harmon Kardon avr-635, and will end up getting a power amplifier to run my home brew speakers (they are not very efficient and the impedence dips below 4 ohms).Then I got thinking if I am getting an amp why not get a preamp processor?now I have a tight budget and if I go with the pre-pro it would have to be an older unit.Now I dont care if I am only getting 5.1 over the 7.1 that the receiver has to offer.I am more interested in getting the best sound possible. What technology would I be missing out on by getting a 5-7 yr old processor?What I dont like about most reviews I read on processors is that they have glitches. I dont want to get into something that I have nothing but problems with, It will have to last me 7-10 yrs before another upgrade.How much better do seperates sound over the a/v receivers? A few older models of processors I looked at on ebay were B&K, Outlaw, Proton, Rotel, Denon, Marantz, and proceed.These units ranged from 150-400$ and were 1000-over 3000 new.All in all I am most interested in the following features: Adjustable crossover settings, on screen display, at least 5.1, and the ez-set eq feature with mic on the H/K probably wont be found on older processors will it?So would it be a waste of money to buy an older top of the line unit ? I dont know much about the seperates but I know they are better than all in ones. How much better?I will be running in stereo mode till I get rear speakers and another amp too.What does everyone think? Any tips for my upgrade would be appreciated. Thanks Mike
E-mail royxc800@aol.com