Hey Remi,
I bought a Volt the end of last year. Knowing Tiffen has (admittedly) had some problems with the Volt, I think you're on the right track to continue to carry a spare. I went a different route, purchasing the new Volt 1 3/4" gimbal, and the new XCS 1 3/4" carbon fiber post with PRO connectors. I had a XCS 2" carbon fiber post with PRO connectors before, with a XCS gimbal, and I keep that as my backup post / gimbal. I also am holding onto my Wave for now.
With all the above, including a MDR4 (I still had an MDR2 on my sled), cases, cables, etc... it was close to $30K, but I have a solid system and am basically state of the art from an equipment standpoint. People are starting to ask for a Volt, but that's not why I bought it. It was really Garret's and Geoff Haley's comments on the Walking Backwards podcast that convinced me the Volt was more than a crutch for guys with bad horizons. Flying neutral balanced and removing all pendulum effect is very nice. I've also lightened up my sled quite a bit. Where I used to add weight to cameras for stability, now the Volt provides that stability in a lightweight setup. Aside from the operating advantages, I think the Volt will extend my career, much like I feel my Klassen harness did.
The downside is that the Volt is not as robust as PRO or XCS gear. You will have issues, and it's frustrating. I've had more equipment issues in the last 4 months than 30 years of operating. Some of the issues were my lack of familiarity with the best way to setup and dial in the Volt. Tyson at Tiffen has been very responsive about working with me on this. But some of the issues were straight hardware failures (I had a motor go bad in the first month) and issues related to design flaws (like an assymetrical gimbal).
When it works, I really am coming to like the Volt features, particularly changing headroom via the push of the button. Larry McKonkey's button extender is a must.
I'm sorry I don't have any experience with modifying a PRO gimbal for the Volt. I would suggest sending both post and gimbal to Tiffen for fitting, which I did. If you decide to pull the trigger, give me a call and I'll point out a few deal points.
Best,
Mark