Powered sub suggestions to mate /w Harbeth P3ESRs

REL subwoofers have a reputation as a good match with Spendor and Harbeth speakers. Looks like there are a couple of units in your price range listed in the Audiogon classifieds.

I am using a REL with my Harbeths and could not be happier. (unless I had two RELs)

You might want to look into a Velodyne SMS-1 ($450) or SVS/Audyssey ($750) sub controller. My guess is that, together with your existing sub, this will provide the biggest incremental bang for your (half kilo to kilo) buck.

Good Luck

Marty

PS - If you search these threads for SMS-1, you'll see that I've written pretty extensively about this device.