if you are serious about the 2 ch thingy... I've yet to hear an int that surpasses a preamp if both are of equal value.
So an active line stage preamp would be my suggestion, and one with tubes too.
if this is some sort of compromise wherein another amp as well is being sought... then perhaps you can find a good int to fit the bill. There's sure plenty of them around for $1500.
'Course, a lot too depends on the sort of sound you are seeking for the music you prefer.
maybe adding a nice 2 ch amp to replace the multi ch one you have should be a consideration.
That's where I'd go first. Something like the Butler TDB 2250 preowned for a tad more than $1500..... or an odyssey Stratos souped up for about that new. preowned, for less of course. Both would provide more power and better sound quality. With the Integra proc I'd lean towards the Butler tube hybrid.
my multi ch Butler sounds better than my Stratos Plus amp... but costs more too.
having owned a number of BW units... they do enjoy power. mo' power? Mo' betta.
Exchanging in better amps is the usual path when starting out with a multi ch affair and desiring better 2 ch audio... and normally, it's the safer softer easier way to go. Once the newere better amp is in place THEN choosing a better preamp gets a bit more defined.
Good luck.