I'd be tempted to go with a breakout board, individual axis driver boards to suit your stepper motors, PSU(s) and an enclosure.
Having succesfully added a 4th axis to a 3 Axis Routout CNC box, but only after I'd messed about with and sent back a 5-axis all in one board from china, I'd go with as many discrete parts in the system as possible, that way when a part fails that's the only bit you'll need to replace, if you go for one morev axis than you need you'll be able to repurpose the spare in the event an axis fails on a Sunday morning ;-)
ATB,
Nick