Printrboard scalability limitations?

[Roxy]

I was using 1.6.5, I believe, with teensy.

Are you thinking this a library issue?

I don't know for sure. I ran into problems with V1.6.5 with the Marlin branch. MarlinDev works with 1.6.6. If you get the 'Hourly Build' of Arduino and install that, you may be OK.