Subwoofer with Unison Unico

Yes.

You can choose a sub that has speaker-level inputs, or solder up your own voltage divider network with speaker leads for the input and RCA jacks for the output, or get one of these:

http://www.audio-magus.com/SubLine_Subwoofer_Connector_p/slv2.htm

In either case, you essentially wire the subwoofer's amplifier in parallel with your speakers. There will be no effect on your amplifier or your speakers.

Duke
dealer/manufacturer

REL sub would work since it is designed to use a high level input from your speaker outputs.

I had a sub connected to my Unico at some point using speaker level connection.

I simply ran a second set of speaker cables from the same terminals used for the main speakers (in other words, from one set of terminals, i ran two different sets of speaker cables, one set going to the mains, the second set going to the sub)

No issues.