back up and running
To Howy: have not been using the monster speaker selector with the Denon setup. That was with the Sony HTIB earlier on.
To all: Ended up trading up to the denon 2106 which seems to have solved the problem. Can drive all speaker pairs individually and together as loud as I can bear...Maybe that 1804 was just sick from the start.
Regarding the impedance matching, given my current setup of downstairs on A, upstairs on B, outside on Zone 2, all being powered through the 2106, are there any other precautions I should take? I realize perfect world is having a separate amp for zone 2, but the current setup solves meets our needs for now.
Thanks again everyone!