Tube pre amp with 2 outputs for Biamping

Sonice Frontiers Line 1, can't lose...

The Hovland HP-100 has two set of outputs. There are a few used available. If you are into vinyl with the phono section included, it becomes a good buy.

Good luck

The Jadis JP80 and, I believe, the JPL have two outputs. They can be "reasonable" (at least the JPL) in the used market.

Anthem Pre 2L is reasonable. Can usually find one for 550-650 on Audiogon. Also some Rotel units have two sets of outputs. You might want to be careful. Some of the manufacturers that use two sets of pre outs just "y" off the main pre out of their unit to get the second one. So although you won't be using a "y", the manufacturer did. (Sometimes)

My Airtight ATC1 has two sets of outputs. If you can find one used they're usually under $2k and they sound great.