Classe SSP 800 will be superior sounding and lot more refined sounding than the Anthem AVM60. If you don't care about 4K video, Dolby Atmos, DTS-X setup, go with a used SSP 800.
However, the Anthem has a phenomenal ARC2 (Anthem Room Correction). If you want superior room correction go with the Anthem AVM60.
For both stereo & multi-channel music the Classe will be way superior more musical sounding preamp processor than the Anthem AVM60......hands down. Especially you mentioned earlier that you like to listen to 5.1 SACD off the Oppo. But the Classe SSP 800's DAC does not decode or support DSD via HDMI, so you will have to run multi-channel analog audio out of the Oppo into multi-channel analog audio inputs on the SSP 800 and set the SSP 800 in analog bypass mode. The SSP 800 is a superb sounding preamp when used as an analog preamp especially coming from an AV pre pro. This is the advantage of the Classe over the Anthem AVM60.
For movies only, still the SSP 800 will perform better when properly calibrated using its manual PEQ (not my favorite) and make sure your room is well treated and speaker placements are spot on.
The newer Classe Sigma SSP that was recommended by dmk_hifi is great but lacks multi-channel analog audio inputs that will be needed for your multi-channel SACD playbacks since the Classe Sigma SSP's DAC also does not decode or support DSD. And I wouldn't recommend converting DSD signal to PCM in your Oppo and output it in PCM via HDMI.
Fyi, in my dedicated reference high end home theater room I used to have the SSP 800 for numbers of years and have had thoroughly enjoyed its sound quality so much for surround sound movies which also includes bluray concert films as well as bluray/4K UHD musical films/movies. But then I wanted Dolby Atmos & DTS-X setup so I sold the SSP 800 and got a Lyngdorf MP-50 instead. While the MP-50 is equipped with phenomenal Room Perfect room correction but I preferred the SSP 800 especially for those bluray concert films & bluray/4K UHD musical films. The SSP 800 sounded more musical. As rshad0000 has stated earlier that the SSP 800 was able to pull you in more into musical scores in the movies better than the Lyngdorf. In comparison to the Lyngdorf the SSP 800 sounded fuller & had more body to the sound smoother and more refined and tonally the SSP 800 was more balanced compared to the Lyngdorf.