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The Powermate is to be used visually as is with either 2" eyepiece (remove 2"-1.25" adapter that comes with Powermate first) or with 1.25" eyepiece. There is a special Tele Vue T-ring adapter that is screwed to the top of the bottom part of the Powermate when used photographically, (replaces visual top).
Why do you want to use 2" only eyepieces? The is no advantage at higher powers in fact you have the disadvantage of all that extra weight. A 31mm Nagler and 4x Powermate will give you a 235x which is equivalent to using a 7.75mm eyepiece. You will get 82 deg apparent field but you can get the same with a 7 on 9mm Nagler at slightly different powers but a much lighter solution. An 8mm Ethos will also give you a 100deg field and yet is still only 1.25" but has the convenience of a 2" skirt should you not wish to use a 2"-1.25" adapter. If you are using a coma corrector then that is even more weight.
Note going higher power than an eyepiece between 7 to 9mm on your telescope will demand exceptional seeing, good optics, good collimation, good thermal stability of your mirror and no local heat sources in your optical path, e.g. warm driveway, neighbours fireplace etc.
You have a Baader 8-24mm zoom which is an ideal range of powers on your telescope; 228x to 76x. A 31mm Nagler will you 58x and 1.3 deg true field but at 6.9mm exit pupil which requires dark skies. An alternative would be a 26mm Nagler (if you can find one) giving 70x and 5.8mm exit pupil and 1.1deg true field. A 21mm Ethos would give 87x and 4.7mm exit pupil and 1.13deg true field. Note all these calcs are without Paracorr. If using Paracorr divide exit pupil by 1.15 and multiply magnification by 1.15, (or multiply focal length by 1.15 before doing other calcs.).
At the high power end eyepieces between 6 and 10mm would be useful but 6 to 7 only under exceptional seeing. You can use your Baader at the 24mm setting with your 4x Powermate to determine if 6mm is going to be useful. Note given your focal length of 1828mm a 2x Powermate would be more useful more often. However after saying that I once had superb views with a 10.1" f6.4 with 35mm Panoptic and 4x Powermate giving 187x. (It was top heavy though at low altitudes). I now have smaller shorter focal length eyepieces which are more practical.
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