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I thought I'd pass along my attempts to acheive good intonation with the Jin Bao Cimbasso.

With the common tuning of the 4th valve to Low C, G, and the 5th tuned to give a good low B flat ith 1,5, I get the following results

Low B, F#, quite sharp played 2,4, and slightly flat with 2,3,5
Low A is flat with 2,3,4 and not easy to lip up to pitch, no other valve combination comes as close.
Low A flat is good with 1,2,4,5
G is quite sharp 2,3,4,5
Low F # is good 1,2,3,4,5

A version of Roberts tuning
Tune so that the 2,4 combo is well in tune, then push the 1st valve trigger all the way out, tune the 5th so that low B flat is in tune. Then you have the following:
G, low C-1st and 3rd with trigger all the way out
F#, low B 2,4
B flat 1,3,5 with trigger all the way out
A 2,4,5 pretty darn close, very slightly sharp
A flat 1,3,4 plus trigger all the way out.
G 2,3,4,5, a little sharp but much better before
F# 1,2,3,4,5 a little flat but close

Over all this gives better average pitch, but I find that these valve combinations a little harder to actually use, also I don't really like having to extend the 1st all the way for c,g as these are commonly played notes.

If a trigger or handle was put on the 4th valve slide to be able to extend it about an inch and a half while playing then it would be possible to have the best of both fingering charts. This would give the following with even better overall intonation, with everything within an easy lipping range:

G low C-4th
F# low B-2,4 with 4th extended (2,4 or 235 would still be there for more technical passages)
B flat 1,5
A 2,4,5 with 4th extended
A flat 1,2,4,5
G 2,3,4,5 plus 4th extended
F# 1,2,3,4,5

The 4th trigger would be used only for 4 low notes, leaving the 1st for pitch correction in the mid and upper range. The 1st trigger seems to need to be in only for top space G and F#, top line A and A flat are better 12 (with trigger) and 23. BTW since the 1st trigger only needs to be in for the top space F and F flat, and since it needs to be out 1/2 to 2/3 for most other notes, you could achieve intonation comparable to most valve instruments if it was reversed, so that it was always out in a good compromise position for a 1st, and only moved in for the G and G flat.

Some have found that the C above the staff is far out and needs an alternate fingering, I too found that this was true using several tuba mouthpieces, including ones shallow enough for cimbasso. However when I tried using a dedicated contrabass trombone mpc, the upper partials lined up much better so that high C is now well in tune open. I'm using a JK 2C with a JK euro tuba adpater, As a bonus the sound is IMHO clearer, more like a contra trombone, less like a tuba on a diet. I realize that most tuba players won't go this route, preferring a tuba sized rim, and that will become the norm. But it's interesting that this cimbasso plays easier, better in tune, and with a clearer sound with a contra bass trombone sized mpc. Of course I expect your results may differ.

Hey Joe. We pretty much have the same horn, albeit from different distributers. Mine has a tendency to pretty much follow the same patterns that you outlined. I find that I deal with them a little differently and use fewer alternate fingerings and tend to lip in the direction I need. (On my BMB F tuba I recently installed a MTS device which mechanically can handle any of the intonation issues.) but I haven't figured how to pull that off with the enormously long tuning slide on the Cimmy.(Maybe that's this Minnesota winter's think tank project.) With the mouthpieces I tend to use, the result is rather forgiving. While I do like a shallower solo mp for its more contrabass trombone sound, I find it less forgiving than something like a Helleberg 2. So I've pretty much decided to go with one that makes pitch adjustment a bit easier. Maybe I'm just lazy.
In the good old days, for about 45 years, I sported a MW 46 with 6 valves, but I set it up to use basically just 5 valves with the 5th as flat whole step. I only kicked in the 6th (1/2 step valve) for low F sharp.
So low C was 4 and B nat was a lipped down 2 & 4 (depending - sometimes with a 4th valve pull) That was an easy pull with the LH thumb. From there on down, I fingered each half step a simple 1/2 step lower, also with the thumb on the 4th valve. Then as I mentioned, f sharp was all 6 valves. This, for the most part, kept the fingerings at least in the same sequence. That is pretty much the same set up I use for all my horns to this day. Being dyslexic and ADD along with eye muscle issues, I find having to think too hard on fingerings really gets in the way BIG TIME. The open middle C on my cimbasso is actually a pretty good note. It want's to lean a tad flat, but not too hard to keep on pitch.

I'm figuring if I could shorten the inner 2 sleeves of the mts, and shove the cut offs up in the slide and have say, about a 6 inch functioning pull on the slide, I could probably work it with a spring loaded trigger. This would be my ideal solution.

I'm getting it back from the Minnesota Orchestra tomorrow and I will be interesting to hear what Steve Cambell had to say about it after messing with it for 3 weeks.