Picked up a domino xl700 and all 3 domino boxes today and ordered the Seneca imperial thickness gauge + shim and the d500 cutter adaptor which should arrive early next week
I would be interested how you get on with the adaptor, I purchased the 700 a couple of weeks ago , I also have the 500 and I am curious how many 700 owners get by with just the 700.
I have used "just the 700" for years. I really like it in all aspects. The adapter is great and for box work I mainly stick to 5 and 6mm bits. It hasn't steered me wrong yet!
I would say that the only complex task is if you have to make a mortise in the field of a panel (to attach a shelf/etc). It takes a little more thinking and if you do it enough, you will come up with some jigs to make it easier.
I love the heft of the machine and how smooth it all works.
If you do a lot of mixed work (doing 5 & 6mm work plus some 10mm work) on a single project, then a single 700 might become a PITA pretty quick. If not, it is a great medium without any real compromises.
Oh, and if you mostly do 4mm stuff, stick with a 500.