Internal sound cards are fading fast! Same with firewire. So no new drivers for most (except RME for now). An EMU 1212m might work but don’t pay more then $80 for it.
If you can get the HDSP9632 for $200 that would be a good price. Easy to sell without to much loss later on. But there is a chance you won’t need to upgrade for a few years if the RME works as expected. I have an even older machine, a Q9550, OC’ed to 3.6ghz, that still does the job. Unless you do video coding newer cpu’s don’t bring to much and your CPU is easy to over clock.
I have a feeling with USB3.1 and thunderbolt (also 3 versions) and USB C that buying an interface for a long and stable life will be more difficult. But since you don’t need many ins and outs an RME babyface might be a solution! USB2 might be here to stay (not on apple though…)
What do you mean by revision, firmware upgrade? sorry wrong card not the hdsp9632