"I would not do the ACT 3 as technology has moved on... I would do a Denon 3806 with room correction and keep you current Preamp." (cytocycle)
Actually, technology hasn't moved that much! Infact, for all the applications you'll use, nothing we've got right now is really supperior for your movie applications than that old outdated ACT 3! Infact, I've got a piece that uses 24/96 and 24/192 Dac's in it, and it's not really better for DD/DTS movies than my old ACT 3, just a tad quieter in the signal to noise department. Otherwise, my old Act 3 was just as potent!
Look at it this way, everyone's either playing CD's, which are 16/44, DD/DTS movies, which ARE NO HIGHER IN REZ, and analog or Hi rez audio sources (which is covered by your 2 channel setup!). Nothing right now in a processor is going to beat up on the old Act 3, and similar!...just more bells and whistles mostly.
HOWEVER, I will definitely conceed that some of the newer processing for Parametric EQ, like in the Denon, B&K, Sherwood, etc, are VERY VERY practical and effective in most setup's, yes!!! If you can't get your speakers/seats to where you're getting reasonably flat response from your system, then yes, you will definitely benefit from this sort of acoustical help! Still, if you can set up speaker properly, then you can get around this. However, the piece in question still has to sound good on it's own. Receivers are mostly a sonic compromise, with some exceptions (i.e, the Arcam).
If it were my money, and I had a good setup, and didn't want to spend a bunch, I'd not hesitate to stick in another ACT 3 in my system. I've owned 3 or 4 over the years, and did what you're doing, which was loop em into an auxilary, tape loop, or "bypass" input on a 2 channel higher end preamp for music dubties. Works great!
Good luck