Velodyne DD15 - worth repairing the plate amp?

How good is my Audyssey built into my receiver setting up the sub in my room?

When using the built in plate amp, should I set up with Velodyne hardware/software (and how to disable Audissey/Receiver for the sub only) or switch off Velodyne and run full Audyssey? Or both. I need/want to run Audyssey for the other channels (I do listen to SACD and Stereo). Receiver on my office system (where DD15 currently is used) is my little Onkyo TX-SR353, which uses AccuEQ:

Onkyo TX-SR353 comes with AccuEQ room correction system and includes the calibration microphone.

• AccuEQ: First, AccuEQ detects the presence of speakers and evaluates the impedance of each. Next, it pinpoints their distance relative to the main listening position using the mic and sets suitable sound-pressure levels. Then it selects the optimal crossover frequency so that deeper bass rolls smoothly off to the subwoofer. Finally, AccuEQ performs frequency response equalization based on room-acoustic and speaker data collected via microphone. The sound-field is now tailored around the listening position, resulting in a more immersive and realistic in-film experience.

Usually, unless things have changed, Audessy doesn't do that much to equalize subwoofers. And I would also assume that Velodyne's EQ works more closely with it's internal amp. But I could be wrong because miniDSP is supposed to work great for subs.

Goood to know. Looking forward (hopefully soon) to get plate amp back from EBC and do a comparison switch: Audessy with external class H amp vs built in Velodyne optimization and amp. 

What settings on the receiver do I need to choose when running Audessy for 5.1 (on the 5 and not the 0.1)?

I would just run Audessy normally then go into to manual setup and set the sub's xover higher than Velodyne's internal one. Adjust mains if possible to match the sub.

I need to read up on how Velodyne's software/hardware works. Does it have an equalizer? How does it measure the movement of the speaker cone or how does the feedback control work? Or what crossover frequency the Velodyne uses (fixed? or adjustable based on measurement with their mic of in room accustics)?