Thanks Frank and Pauls
I've been doing some research on the distances. MPCC needs 55mm backfocus, the 583ws has 35.6mm from sensor to T thread, need to take off 1/3 of filter thickness because they change light path so for Astronomiks filters that's .33x1mm=.33mm, that's leaves 19.7mm. I've ordered a 20mm T thread extension tube from Edmund Optics and that'll be within the tolerances as I understand them.
Paul - Sorry, I thought I'd posted the subs info. It was only 2x5mins at -10deg. Very impressed with the low noise.