Hello all, Sincere thanks for the advice. Its been something of an education!
From what I've understood, this is kind of thing to what I've been experiencing on occasion. However I'm just finding it very hard to believe that this is the way the denon is "supposed" to sound? If so, I feel pretty sure it would have been picked up in a review / topic of some kind. I would also question the logic of including DSP modes at all as it would be a complete waste of time.
Let me iterate the problem. Everything is OK with a 5.1 source, stereo, 5 channel stereo, and direct (regardless of the source) (no DSP type processing at a guess?) All other modes (from memory, DTS: PLII, Neo 6 etc (both cinema and music modes) rock, jazz, game, matrix) illustrate the fault on an irregular basis with stereo inputs (via TV, DVD, CD & xbox (less with CD). They do however work fine some of the time on the same source and material that later illustrates the fault. Which is the most annoying thing in this situation. The easiest way to replicate the fault appears to be cycling through the different sound modes. The sound can be anything from very quite, but often loud, crackling/screaching to a boomy echo. Not the echo type effect as in the jazz and rock modes, but a repeating type stammer. The sound is very obviously wrong!
I thoroughly checked the cabling (used analogue and digital) and their immediacy to power cables. I even switched off mobiles, wifi, and cordless phone!!!
I'm no expert obviously, but as was pointed out earlier, I would of expected either RS or Denon (perhaps both) to be cogent of these issues if this was an accepted processing flaw. I recieved no indication at any time that these faults were to be expected under any conditions.
I'm just hoping that RS can replicate the fault at their end.