Drew,
95% of all the jobs I have seen on the GT-381 have been done in 1 pass. There are times when doing a left chest design that the software will put a delay between the white and color layer. I have also been told by someone that if you max out the sliders that it does 2 passes. I just have never seen the need to do this to determine if it is done in 1 or 2 passes.
Stating that, you might want to come to the Arlington NBM Show in 3 weeks to check out the new RIP. You have more control over the RIP than the GT driver. One benefit we have is you can do a print that uses these 2 passes:
Pass #1 - 600 x 600 white underbase pass only
Pass #2 - 1200 x 1200 white (at 50% max ink) + CMYK pass
The benefit of doing this is it cuts do the print time by 25-30% compared to a 1200x1200 print using Mask 3 and Highlight 6. So the RIP allows the 2-pass method and still gives you a higher output.
Just something to consider. Best wishes,
Mark