The 4000 that I was using was returned to my son after I got back my Sunfire TGIV from restoration.
I did like the feature on the 4000 for the AC PU especially when button 19 is engaged. This is the Correlation-Automatic Threshold system that self-adjusts. Everything rolled into one unit which was kind of nice. I can see why you are leaning toward the 4000.
With the Sunfire back in the system I introduced a PL1000 Series II to take care of my Vinyl and tape collection just as @Dennis47 suggested and has worked just fine.
I don’t use the built-in phono preamps in the Sunfire because of the distance of my TT from the Sunfire. I employed a Bellari PA550 3-Channel Phono Preamp into a switch box. The Cassette decks also go into that same switch box and then the output from the switch box goes into the PL 1000 II before going to the Sunfire. Sounds like much but it works just fine.
For my case this is how I incorporated the feature that I liked in the 4000 into the Sunfire. Not everyone will like this system but for me it’s how I blended the old with the new, or not so new.
As @AndrewJohn pointed out there is a distinct advantage of having proper external “Carver Amps” for the surround mode when set up. For one thing you can mix and match amps as they are acquired and placed into your system. For my current system I have a similar arrangement in that I have a dedicated amp for each of the five speakers. Two 35 and three 15’s.
I ventured down my road a little different than someone else. I kind of like separate units that just do one job and hopefully do it well. With my present equipment, and if I did not have a preamp, I would lean toward the 4000t.
But then again if a good 4000 crossed my path I would be hard pressed to resist it, saying this will work just fine in the “D” system that I can build upon.
In the end no matter what you choose, you will enjoy the music that it produces.