Yes about the LZX TBC. If the rack tbc you have has genlock input or sync I think it will do the job.
I would probably get some cadet processors and crosfader pcb/panels instead of the passage to cut cost and you can place them around your system better. A cadet scaler or two is not a bad idea for putting audio eurorack gear into the video path but a panel of passive jacks/10k linear pots would work too and in some ways give more control once you get the hang of them.
Any signal in the video synth goes into the mapper and you get crazy "toasting" effects like solarization. Think of stuff you do with the videonics colorizer and make it better(cleaner) with more control.
The vco's give you shapes on one level and modulation sources on another and both at the same time if you want. The prismatic rays are particularly good at making shapes to my taste over the original vwg's but they still have lots of uses too.
I recommended two prismatic rays because I was told the more oscillators the better and after I got several I tend to agree. The prismatic rays can also be used like a keyer in awesome ways.
I think the cadets are the way to go.