Iñaki. thanks much!
It seems that TOA-150B + flattener/reducer is the way to go. two more questions (stupid ones)
1. Does anyone have a color photo? for some reason found only a couple photos on astro bin with TOA 150B and QHY600/ASI6200/16803
2. (a little bit off topic) what do you usually do with wi Tak stock focuser? Please excuse my ignorance - never had a TAK. Are you attaching some motor? or remove it and put another (WR35, FT3.5)? I assume that all these flatteners designed to pair perfectly with TAK stock focuser - so which motor are you using?
I will have some photos with the QHY268M and FLI 16803 on the TOA150B as soon as I can get the sky to clear out. I do not have my IMX455 chip camera yet. That will probably be another month or so. I should have both the TOA67 and TOA645 flatteners to test as well. I should mention that the Reducer 0.7x for the TOA series does not work well with small pixel full frame cameras. The older 645 TOA reducer might work a little better, but it was discontinued and is very hard to find. I am hoping they make a new 645 reducer with smaller spots that are more suitable for modern CMOS chips.
I really want to use the stock focuser on the TOA150B. It is very nice, and has a manual camera rotator on it that is very sturdy. For motorization I put on the Sesto Senso 2 motor from Primaluce Lab. It connects up nicely to the stock focuser with no need for extra adapters, since the TOA150B focuser shaft is 25mm. If you get one and do the same be sure to use the gold bushing and not the green one. The gold bushing allows for the grub screws to set in fully, which is important when you connect the motor to it. The green one they don't seat in fully and will prevent the motor connection from seating all the way in.
I just need some clear skies to test out the TOA150B as I have it now. I am optimistic it will work well.