Velodyne DD15 - worth repairing the plate amp?

rwwear: what does it do? similar to what audyssey does (measure room sound, make correction in time and equalizing frequencies, automatically)? 

It's an outboard version the one built into the Velodyne DD series. You can use it with any sub though. Can be used as a replacement for the Velodyne built in EQ if needed.

https://www.outlawaudio.com/products/SMS_manual.pd

This is the Hall brothers first release of subwoofer Equalizing I believe based on the Texas instruments platform using Velodyne custom designed parameters. Shortly after the SMS release the Digital Drive was rumored with an advanced servo circuit, driver and cabinet. The component SMS may have been geared toward supporting the companies legacy products and third party subwoofers?

Despite its age the SMS can provide more detailed capabilities than a number of current low frequency processing designs.

It's a great product if you want a simple way to set up subs that don't have built in room correction.

Minidsp does more but requires a computer. Once set up it doesn't anymore though.https://www.minidsp.com/

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.