I considered the following:
Setting ampsim to cabinet off and on, output =line. Did this for every option for output.stack front, combo front, combo power amp, stack power amp and line out. Per Todd and Bruce below, i have left the cab sim on - yet no cigar.
The receiver takes analog in (red white). All sound terrible - like solid state amp i got with my guitar amp combo from lyon by washburn. Bass is excessive , sounds very digital. Zoom sounds wonderful on headphones and on my blackstar fly 3watt via aux in. Interestingly, i record with tascam dp006 and it sounds perfect exactly like the headphones.
Another example: i can get a nice sustaining lead tone with my headphones on, but it sounds like very little sustain through the 5.1
what am I missing. Receiver is a Harman kardon in 2.1 mode (polks+pioneer). I have checked to make sure there is no funny eq, bass boost or other stuff. My sneaking suspicion is that because zoom combines the line out with headphones the output level is actually not true line out. Yet it works awesomely with the tascam. Completely befuddled.