Hi!
I wanted to write a little longer reply but Safari on my iPad kept refreshing every time I changed tabs to look something up.
So here we go:
Between that "shed job" I got the DTS 400 for and now, I got my hands additionally on a used DX 93 E via ebay that I put a little work into.
My, very personal and limited to my experience, opinion is that the DTS 400 fits my hand and work "style" better than the DX 93 E however the options for the DTS 400 are limited to that one sanding pad, whereas with the DX 93 E you can get also softer sanding pads - and, maybe most important, a slat sanding pad. If you're going to need the latter, the DX 93 E is basically the only option.
If you don't need the slat sanding pad - the Rotex RO 90 DX might be another option as it combines the options of a triangle sanding plate/pad or a round one of 90 mm diameter - which can be a plus when sanding surfaces. But I don't have any experience with the RO 90.
Since Festool puts both, the DX 93 E and RO 90 into the category of rough sanding - and knowing what the DTS 400 can do - I'd like to recommend the DTS 400 for what you want to do. Definitely get an extra sanding pad or two if you're going to use the tip a lot.
Kind regards,
Oliver