mdrew,

If it's truly line-level signals you are using (like a couple of volts, from the pre-outs), then you might find a used simple 6-band equalizer on Ebay. Get one with a bypass switch so you can switch it out of the line and compare the EQ's sound with the unequalized signal. Some of the old brands that were decent were ADC, Technics, etc.

If you are using the Zone 2 speaker outputs, then an Equalizer won't work.

Regards,

Alan Lofft,
Axiom Resident Expert (Retired)