Are you sure that the red and white RCA terminals labeled "AV outs" (just to the left of "Zone 2 out") cannot be used as pre-amp outputs?
So, you are not concerned with driving he Magnepans?
If not, I would expect the 675 to do as fine of a job as any $500 amp. However, if you are simply determined to get an integrated amp for the CBM-170's you don't need anything special.
AT $500, if you are willing to go with a stereo receiver:
Stereo receiver with built-in Wi-Fi®, Bluetooth®, Apple® AirPlay® 2, HDMI, and HEOS
www.crutchfield.com
For a Integrated amp, this one is $419 reconditioned (or you can pay $550 for a new one):
Yamaha Factory Refurbished
www.accessories4less.com
Neither of these will do a very good job with integrating a subwoofer!