Hi Guys...
Very interesting topic that I just found...
I experienced the same thing... and I'm pretty used with amps and PODs...
A couple of years ago, I used to play with a Hughes and Kettner preamp proccessed in a Digitech GSP 2101 sent in a Crown amp DC-300, driving 2 Fane cabs (in stereo). I had a great guitar sound ...
(I still have all that gear...)
For a transport reason, I would say.... I bought a POD Pro (back in around 2002), expecting to have everything in one box... That idea was to eventually plug directly in the board and get my guitar sound in my monitor mix... So, I would only have to carry my Pod and my guitar...
Already, I experienced the same problems that you describe..
Then I bought the HD500 couple of years later that I worked on for the past three years trying, as you described, to get THE TONE... I drive the HD500 in Krk V8 studio monitors... and I tried everything, from trying the main setup in Studio/Direct mode, to Combo, Stack, etc. using one amp, two amps in parallel, EQs, I even tried with the POD through the FX Loop in order to get more DSP to use another EQ, etc, etc.
This device is so versatile that I can't believe that I can't achieve to get a proper Hi-gain tone... To my eyes, this HD500 box is like having a complete music shop were you could try to mix everything, from amps to cabs to mics...
So, there should be a way to make it sound really good...
Usually, I try to boost lo-mids around 160-200 Hz, cut around 1kHz and 2,5kHz but I still have some zzzzzzzz in the tone...
Clean sounds are not so bad, though...
Really interesting to read your posts,
By the way, I've been really interested reading the posts from Iknowathingortwo ... I feel that we've been through the same hard quest...