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

Al: I wish I had your knowledge. I’m too simple on audio and don’t want to go a little funky or compromise in any way if I was buying uber ARC products. That’s my problem. 

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