10k would be my choice, although the PBC is pretty flexible about that and calibration will correct for most pot values.
The one you linked to says reverse audio taper, which would definitely cause a problem. Look for a pot that specifically says linear taper, otherwise it's not going to behave correctly. On that site, I only see dual 16mm pots that have linear taper - those would be fine, you would just use one section of the pot.