Hard to believe the Plinius is having a tough time with 805's, but if you say so. I have dual Mk3's and one of the main reasons is to go fully balanced, which is not possible with RCAs.
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1147688305&openflup&11&4#11
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1147688305&openflup&11&4#11