it depends on what you got.
if you have a midi rig with your protools, you could use that to send midi to the Dark Energy, and in turn use it's outputs to control other synths.
but you'd lose some control over the Dark Energy itself, there's only so much bandwidth.
You could add a Kenton then, no problem. There's USB ones too.
Have a look at "Expert Sleepers" modules (ES-3, ES-4), and their "silent way" plugin. Perhaps that works as plugin for protools as well.
Or MOTU Volta, and one of their interfaces.
Both use common audio outputs, which are near sample accurate. no more midi delay and sync hell! This doesn't work with midi gear though...
Or... if you plan on using outboard sequencers, check the "Innerclock Systems" or SND ACME4 products which do clocking without latency.
That does work with midi gear (but only clock).
I have an ES-3 coming and just ordered the ES-5 expansion. Yet I use midi sequencers (MPC, Logic, E-mu) as well and midi-CV. Since I don't want to be dependent on a DAW anymore to write music.
there's been a couple of threads about this, do a search, and read up yourself. (don't be lazy or you'll invoce the wrath of the godess of the eternal patchcable