Thanks for the considered answer Dennis - I appreciate it
I guess that, being only 355mm in focal length, I'm not going to use the Tak for planetary - except for the moon maybe. I was wanting to get a narrower FOV than that which I get with the DSLR alone attached to the f/6 flattener - primarily for objects such as B33 and M42, 47Tuc, Eta C and Omege C. I think that this system would be ideal. Being variable, and then being able to choose from a plethora of EP's, I reckon that the range of magnifications you'd get would be almost infinite - within the practical scope of the optics.
I hate to admit it, but I've never known or even investigated whether you can attach a DSLR camera T-ring/adapter to a 1.25" barlow system. Can you?