I had the same problem. I made the following hold downs that solved that problem. There hasn’t been a size yet that some combination of the blocks wouldn’t hold.
I have the one mpcnc and the one laser engraver. I could see where having more than one machine that can do the same job would mean one sat most of the time. I would like a second printer, but only because it’d be nice to print multiple objects at the same time. The cnc doesn’t take as long for most tasks, so less of an issue.
It sounds like a 4’x4’ lr2 might be your best choice. Another option I just thought of would be to have the smaller lr2 in your basement, but build it in a way that you can carry the gantry up to the garage. You could have a larger table up there for when you need it, but let the machine live on the smaller table most of the time.