All of our current stereo amplifers have the same gain so can be used with other amps in the range. Obviously you are likely to get better sound quality from the greater current drive from the P90, however I am sure you would also get a usefull improvement from the P80 if funds don't stretch to a P90.
The other option would be a second hand P85, ebay is probably your best bet for one of those. Or you may be able to find an ex dem unit if you are very lucky.
Regards,
Andrew