So I guess this means you really want an outboard pre-amp for 2 channel audio, right?  

  I think this will be easier to do than getting an upgradeable receiver.  The major reason I got an SP 1.7 was because the receiver manufacturers didn’t offer upgrades.  Well-they did, sorta.  Either you could get software upgrades (only Onkyo at the time) or they SAID they would offer a hardware upgrade (Denon - at the time).  Denon did offer a hardware upgrade on the 5800.  Unfortunately it was 1 year after the initial release (far too soon for me to consider upgrading), the upgrade was a limited time offer (six months, I think, but not sure) and then it was over.  Period.  No more upgrades.  You wanna upgrade, buy a new model.  
 
 I decided to buy an SP 1.7 so I could upgrade whenever I was ready to.  I personally don’t miss any of the bells and whistles because I ended up never using em.  So please be careful about upgrades when choosing your receiver. If you choose a processor in place of a receiver, I believe many manufacturers offer upgrade plans for those (it seems to be the norm).  Good luck! 
