Launched for Yamaha's centennial anniversary, the PRO is almost THE well-known version and an update to the original NS-10M with mainly a revised filter to address the issue/tissue issue many 1980s engineers got hot about earlier in the 1980s.
The PRO still bears its "home" origins in that it is made to stand upright (with a filter placed accordingly inside) and still has a detachable front cover.
Otherwise, it has the big cable terminals of the STUDIO and the same drivers and the very same specifications.
The STUDIO differs in that it is bare and made to be used horizontally with a filter placed accordingly inside.
Otherwise, no difference, but the PRO isn't as common as the 200,000 pairs of STUDIO Yamaha sold between 1987 and 2001.