Upgrading HomeTheater

Upgrading to separates what are some good preamps/processors
and multi ch amps under $5000(new or used)my system now
denon avr3600
denon 2800 dvd
def tech speakers
Check EAD Signiture 8 plus Bryston Amps

You may want to check out the outlaw audio pre processor and amps, I myself use denon with acurus and really enjoy the combination.

some good cables, both speaker and interconnect, can many times improve your sound. used proceed avp-s and krell hts1 are both excellent pre amp's. Lots of good amps out there----min of 100w continuous though. Denon is usually pretty good equipment. Maybe a good subwoofer??
Theta. Hard to go wrong.

I also have a 5 channel Earthquake Cinenova Grand we are getting on trade (buyer went to a Theta Dreadnaught). It is a pretty good amp and will be under $2K.
I also have a great deal on a Tag McLaren 100X5 amp posted here on Audiogon. If you can find the matching processor, that is a truly killer combination that will come in right around $5K. Oh..and the Tag amp is *extremely* good on the Def Tech's.

The Sound Broker
Very very good chioces to consider, in my vast hands on experiences, would be a minimum of the likes of Acurus Act3 and Acurus multi channel amp combo(superb superb...and cheap!!!). Also, Classe SSP25/30 and matching Classe Amp(s)! This is even better choice, and is as clean, clear and detailed as you please for digital sources. Plus the Classe Surround pre/pro's have "dirrect analog inputs" for pure 2 channel analog sources and such...nice! The Aragon Soundstage and amps are more money for similar performance however. There are some other nice considerations in these price ranges of gear, but you'll have to try.
The next stage up at the top will be Proceed AVP and amps, and Krell HTS and matching amps.
Really, for the money, your best deals on the used market sonically are going to be fining the Acurus line or Classe! They will "Garanteed" make you happy, and first choice going to the Classe, for better signal to noise ratio, and "analog bypass dirrect" modes! Really, I don't see anyone dong much better a combination HT/music pre/pro and amp than the Classe stuff! Yeah maybe a hairs breath better in the Krell amp/preamp for digital, but a lot more!
My money is for Classe used...you won't lose.
good luck...