Only one to know for sure if you will notice a difference, buy the amps and have a listen, you can use the Denon as the PRE/PRO and even if you don't notice much of a difference you now have the beginings of a nice seperate system and when the time comes you can just buy a new PRE/PRO with the features you are looking for.

FWIW, others on this site have mentioned better low end and crisper highs with seperate amps.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70