Domino tenons serve two purposes:
* they help to align the pieces together
* they increase the surface over which the pieces are held together with glue, thus making joints stronger
You can use 10 mm thick and 50 mm long tenons, the longest which DF500 can accept to make your doors. In my opinion (but perhaps more experienced people have other view on this), interior doors will be at a boundary between where you can still use DF500 and where you could benefit from the DF700 (XL). Something like 80 mm long tenons available with XL would make your doors even stronger and alignment even better. But as long as it is an interior door, I am thinking that the requirements to the strength of the joinery are not as strict. It is not exposed to moisture and it serves almost purely decorative purposes. I cannot imagine a door assembled with 50 mm long dominos falling apart. Additionally, you can use two of smaller tenons side by side instead of one big tenon.
I own a DF500, and just the other day I had a chance to "play" with a demo XL tool at a dealer. XL is quite of a monster compared with DF500, comparatively heavy and big. Even if it can be adapted to use smaller cutters, I find it hard to imagine how to use it for precise cuts on small pieces, comfortably and without fatigue. It is the same story as with Festool routers - I think most people agree that you do not want to buy they biggest router, OF2200, as "one router for all", even if you can use it with all types of bits and, in theory, for any task. Not that it is less capable, but it is just too big and heavy for most tasks.
