I appreciate both of your insights into my 'issues', here's a few follow-up thoughts I had:
1) the thought of using a pair of LP72's won't work on the Sea Searcher, as they will issue me an AL 80 (I understand the Fling/Spree requires divers to bring their own tanks, so they don't care what size one uses....which is the opposite of the Sea Searcher, where one-size-fits all, like it or not.)
2) I will probably relax more and use less air with the comfort of a pony than if I don't use a pony and worry more about the air issue.
3) I knew the 'soft' manifold concept wouldn't be very 'PC'.....I'm just thinking out loud about doing that versus using a 'conventional' set up --totally independent pony+reg bolted to the side, with no 'communication' with the main tank. In defense of the concept, I would be using a brand-new short HP hose, so I think the chance of a 'blow out' is remote.
4) The 'soft' manifold would simplify my gear (I think) although I'm still looking at exactly how it could be set up. It appears I could access the pony's air without needing to attach any other hoses to the pony 1st-stage, just attach the short HP hose to connect the 2 1st-stages, and simply use the BC / primary 2nd stage/ octo/ SPG/ air-integrated computer run all off the primary 2nd stage as normal...which would reduce the number of loose hoses (and the resulting drag), since I wouldn't have to necessarily run an independent 2nd-stage/SPG off the pony 1st -stage (although I could if I wanted too).
(yes, I do agree there is a sound logic to operating the pony as a completely independent system......and I'm not saying that I won't end up doing just that.......one disadvantage to that would be I'd have to manually inflate my BC, as I can't connect 2 independent BC hoses to my BC)
(also, it might be nice to let my air-integrated computer 'see' all 110 cu. ft. of air available.......so that if in an emergency I have to dip into the pony air reserve, the computer will still accurately track my dive parameters, so I know where I stand as far as nitrogen-loading, safety stop duration, etc)
5) I don't plan any endurance/depth contests, so I have no intention of violating NDL/depth limits....but would like to have a 'fudge factor' built in. I'll be with 15 other divers, and will follow the groups' lead, but I want to guarantee that if anyone has an OOA emergency, I'll be the one donating, not receiving........just don't want to be the weakest-link.
6) Buddy paring worries me, and as diving with complete strangers appears inevitable, a pony would increase my survival chances, as I'm leary of depending on someone I've never met before being my sole back up plan.
7) I wasn't planning to rely on the pony gas to prolong my dives, my impression is that most divers won't even use ponies, so when my buddy calls the dive, I'm fine with that, I just don't want to be the spoil-sport.......just in case my air consumption is really sub-standard, which I won't know until I'm in the water and it's too late to change anything.
8) Sounds like it's a better idea to mount the pony to one side, and add/subtract 2# weight as needed...to reduce drag...and to avoid having that extra pony weight distributed that far out from my body, which I think will tend to pull me backwards in the water too much. I agree the drag will be greater than with my single LP120, but again, that's not an option on the Sea Searcher.
I've got a number of other areas to explore with both of you as well, since you've been so generous so far, as far as what to expect on a live aboard, what to bring, and specifics on dive experiences at the Flower Gardens aboard the Sea Searcher, so I hope you don't mind my asking.
Karl