I have a vintage SAE pre-amp with two band parametric EQ. Using the EPL on my Insight pre-amp I can take signal out to the SAE, run it through the tone (EQ) section and back to the AVA via the EPL with no problems. Wayner is right, though, one needs to be aware of ALL the options for volume control when doing this.....and the fact that the EQ used will probably be way noisier than the AVA circuits......is the extra noise worth the tone control? For me, it was not (even as I was trying to clean up 78 recordings).....I eventually abandoned the EQ.
Cheers,
Mark