Older HK pre power 725+ 770 v 825+870

The Citation 16 is one of the most transparent amps you'll ever experience. Very hard to fault. Built like a tank. You can dead short the outputs without hurting them.

I just got an HK725 pre-amp and am running it through an HK AVR7550HD. Couldn't figure out how to connect it at first. Tried the 725 pre-out connector to the 7550 analog in. But the sound was crackly and inconsistent. Then tried the tape output from the 725 and works fine, but none of the controls on the 725 have any effect. It is just a constant level line output at that point.
I only bought it ($60) for the phono preamp. So, if I connect my turntable (Thorens TD-154 Mk I) to the phono in and then out via Tape Out to my analog in on the 7550 it sounds very nice (via headphone jack on 7550).
Still curious how I can connect via the pre-out on the 725.

Any ideas?

OK I would like to compare them but no chance so i have to depend on others opinions.

my favorite was the 775 Mono amps IMO the best amp ever made by HK better than most of the citation series! One of the dumbest things I ever did was to sell them to my best friend (still going strong)