Hi,
If I got you right, you are using the 3805 connected to the M80s correct? In which case, you would not need another 'preamp' as the receiver itself would have a pre-amp stage through which the input is fed on it's way to the power-amp stage and the 80s. According to what I hear, the 3805 has a pretty decent pre-amp stage. Hope this helps. Thanks.

Cheers!