Which subwoofers have at least a 20k input impedance as required for ARC preamp

Is replacing the preamp a possibility? There are other balanced tube preamps that have no problems driving loads like that.

I have an LS-28 and have ran into the same problem. Switched to a REL sub using the high level input (driven from the speaker outputs) and it works great.  I’m running a Rogue Stereo 100 amp with KT-120s.

@ricwa,

May I know which REL sub you’re using?

Velodyne Plus subwoofers offer line level (RCA) nominal impedance 47K.
Balanced (XLR) nominal impedance 10K. Speaker level inputs.

Refer to their User's Manual for detailed connectivity options.

http://velodyneacoustics.com/pdf/digitaldriveplus/DD+Manual.pdf

@lalitk, I’m using two (stereo) REL T/zeros.  My dedicated listening room is only 11 x 18 and I have two pairs of bookshelf’s I alternate between, Harbeth 30.1s and Revel M126be.  If I had a bigger space I would have gone for the new T7i or T9i which, frankly are better RELs.