2out2sea ... is your OP an academic question or an actual concern based on equipment you own or are thinking of buying? If this is an actual concern, based on Al's post, you may be close. Perhaps a call to the preamp manufacturer is in order.
Btw, I've been there and done this already. I bought a custom designed active impedance buffer for a very similar issue, but in my case only involving the sub-woofer. Check my threads. I doubt my solution would be a good fix if you needed an active impedance buffer like mine to drive your amp. I suspect even if it solved an impedance match issue with the pre, overall sonics might be degraded because you would be inserting an active artifact between the pre and the amp.
Btw, I've been there and done this already. I bought a custom designed active impedance buffer for a very similar issue, but in my case only involving the sub-woofer. Check my threads. I doubt my solution would be a good fix if you needed an active impedance buffer like mine to drive your amp. I suspect even if it solved an impedance match issue with the pre, overall sonics might be degraded because you would be inserting an active artifact between the pre and the amp.