Can't think of any that are going to be $500 or less new off the top of my head, may need to look at the used market. Maybe an Outlaw Audio 975 for a bit more? Parasound 2100?
My old 2ch pre-amps (an Adcom and a Carver) do have tape monitor loops to insert eq or other similar processors but if I understand what your CAL unit is, it's an external dac of some sort that outputs in analog format? Unless you have a graphic eq or a miniDSP to insert, probably don't need the tape loops/external processor loop, just normal analog inputs for your sources.