Hajime: yes this is possible; however, i find that it is done differently for certain characters regarding CH 66B BE...
Zayith: it could be due to a couple things, the main reason being is your timing... and the other reason is what i mentioned to Hajime(he may know this though) but some characters you need to add a small yet fast quick 6 dash input before doing !MCF, although it is very odd and seem very tedious for the amount of time to get it right on whatever character and how it connects on some characters based on size... an example would be on Natsu... Yoshi doesn't require a 6 dash after CH 66B BE, as long as it done as fast as possible, but some other characters(some larger ones and smaller characters) don't or do require a fast 6 dash input before doing !MCF.
I found the shorter(shortest) dash input the more success i have hitting it, the longer the 6 dash is recovering(if the 6 dash is required) out there it will not hit at all, so it must be done as fast as possible while maintaining your 6 dash in or immediate !MCF directly after hitting CH 66B BE ...basically whatever is required to be done for that certain character...but either way it has to be done as fast as possible, with 6 dash or without...don't worry though, this combo regardless of a 6 dash being required can be done on all characters, just need to hit the lab and see which ones you need the 6 dash or not...if the opponents character has his/her back to a wall and CH 66B BE hits, no dash is ever required.