I'm genuinely curious. Is ANYONE able to do this? On every system I've ever encountered, setting Pro Tools at less than 1024 samples while playing anything with over 5 or 6 tracks results in clicks and pops. This is on powerful systems too, including my 4.4 GhZ 64 gb sequencer+slave setup. Does VE just not play nice with Pro Tools? It's virtually unplayable at 1024 samples, because midi notes played in at 1024 buffer results in everything being way off the click. Vienna stuff gets so latent that you have to drag the midi a 16th note before the downbeat in order for anything to match up with click. This is a disaster for workflow and editing since after doing this for five or six tracks EVERYTHING is off the grid and it's a huge mess.

What can I do to sequence at a lower buffer size in Pro Tools (10 or 11, neither one seems to work better for getting Vienna to behave)? What gear do I need to buy? An interface that can handle VE's latency? Right now with VE everything just feels so messy when trying to write.

Is there any way to run at 512 or less withOUT getting inundated with clicks and pops? 

Thanks for the info. I'm just wondering if there is a way to avoid "things sometime get clicky on dense passages" which essentially translates to "the software doesn't work". I'm assuming there isn't way to get VE and Pro tools to work properly as I can't seem to get a response from VSL.

Since you're running a slave I assume we're talking VE Pro. PT11/VE Pro works just fine here at 512 (or even 256 at times), I do run some things from SSD and am not running a slave (modest i7 with 24Gb RAM). While you say "is there any way" they can work together, I say most definitely there is, and for most people they do play nice together - not sure what is unique about your set up. To say the software doesn't work is rather a stretch tbh