I'd like to go on the record to say that after putting in a few hours of time really playing with all of the availble paramters on the amp, cabinet and fx models I am pretty fairly impressed with my Line 6 setup. I have been editing mostly without the computer connection by using only the on board editing facilities and this has forced me to really look at all that is available that I was missing with the HD Edit facility. Things like sag, bias and bias excursion DO make a difference and adjusting the cabinet parameters such as resonance and thump are in my opinion instrumental to obtaining great results. That includes trying all the mic emulations because I am finding the default ones are not often the best choice for me anyway.
I have developed a strategy that is facilitated by this approach because of the way you are forced into looking at these things. It always starts with imagining the end product in terms of BASIC AMP SOUND. This is the foundation as it is in analog amps. So for instance, I just created a classic combination of a Les Paul into a Marshall DSL 100, with the Les Paul set to the bridge position. I always make sure I set the input first to Variax and the second to mic unless I am actually going to try a dual channel setup (which is not very often). Then I set the Variax input and decide whether or not to "lock" the guitars controls -- that is based on the overarching goal of the song (if any) I am gunning for. Then comes the amp setup which again *sort of* depends on what songs you will play with regards to Normal vs Bright channels. In any event, this is when I spend some time with the deep edit parameters I mentions earlier, getting the sound "just so" as they say. When it's there, I immediately save that before I even think about effects. The bottom line is that if I am not willing to play a patch in this state, it isn't done yet because in my view, effects are merely the gravy on top of the meat and potatoes that is the guitar/amp combination.
In any event, earlier in this thread I had expressed my own frustrations and as hard as it might be to believe, disconnecting from the computer made a huge difference for me for the reasons I mentioned. Being forced into looking at the actual machine I am trying to master was certainly beneficial in terms of finding the right sound, but it also carried another benefit, namely distractions from my computer are also eliminated. No email. No forums. No temptation to "look into this or that", replaced instead a full self imposed focus on task. For those struggling to find their sound with a HD500(x) and JTV combination, I urge you to try what I am saying here. yeah, you gotta bend over to twiddle the knobs but it is worth it. And you will get faster as you progress and start knowing where things are in there. Certain things jump out after a while, such as for me knowing that a 57 on axis mic is the best place to start for me, so I head there almost immediately. That kind of thing.
Anyway, hopefully this helps someone out there as it has me.