Your description of your problems exactly mirrors my own. You've followed the same path as I have: changing saddles, altering 'bar height and reach, padding, etc. All to little benefit in my case too. Your comment about "struggling to hold your hands above the 'bars" I interpret as a reference to Steve Hogg's method of determining whether your saddle set-back is correct. As an aside, I'd say that although the "KOPS" thing is a reasonable starting guide for saddle position, it's very approximate and most professional opinion I've seen says NOT to treat it as a rigid rule i.e. if you get a better balance with the knee well behind the pedal spindle, go that way.
I've found some improvement from fitting a seatpost with as much layback as I can find, to push the saddle further back and yes, the tri-bars help, in giving an alternative position, but I can't hold it very long because of the pressure on the perineum.
In my own case, I've come to the conclusion that the problem is fundamentally due to a combination of a lack of core strength and an excess of fat/weight! As I've aged, my musculature has deteriorated (lack of proper training, laziness, etc.) and I reach the point of fatigue sooner, by which I mean that, although I can start a ride full of beans, I quickly get to the point where I collapse like a sack of spuds and all three contact points start to complain.
You don't mention your age, weight, state of fitness, etc. but my best guess is that (sorry to be blunt!) shedding some fat and getting some Pilates/core work in would work wonders. I can say that the Pilates helps a lot - especially with the relief of lower back pain, and since I've managed to diet a stone of blubber off, my discomfort has reduced measurably, although I still can't do the distances I used to. What I have also noticed, counter-intuitively, is that lowering the 'bars has helped. In my case, I did this accidentally, as a result of returning to my old Condor as a "training" (spit!) bike. This frame was custom built for me many years ago when I was much fitter and slimmer but in recent years I'd put it aside as having too 'racy' (too low at the front) a position. I brought it back into use just for short training rides thinking I could stand the discomfort for brief periods but to my surprise, I've found it more comfortable than my newer, more upright frames. I've put this down in part to it's slacker seat tube angle (saddle still further back) but also to having my core tighter when on the drops.
A more drastic remedy would be to try a recumbent - but that's a whole different story .... !
