I checked the Adcom web site and there appears to not be a Adcom 3500. Might you have meant 5300? The 5300 is an 80 watt per channel power amp. If this is what you have then you already have a preamp. If you like the Adcoms sound you might want to get a more powerful Adcom amp. You can keep the one you have for future use, such as the rear channels of a surround system.

I'd suggest something with about 200 watts per channel. You might find a good deal on a used GFA-555.