Doh. I feel really kinda foolish now. I'm not sure where I got the .05ohms for the sense resistor, but I finally got some free time to double checked things and it wasn't .05 ohms. It was .3 ohms. That put my current at 1/6 what I thought it was. Computing with the correct value, 1.5 amps * 8 * .3 ohms = 3.6v, well over twice what I could get Vref to be. I had another pair of driver boards from a previous project that have .1ohm sense resistors that I used for the z-axis. With those, I was able to successfully get to run the two steppers in series but only at 230mm/min. If I pushed it to 240, the default with nophead's modified firmware, they stall out. I'll probably back them down to 220 or 200 as they sound better (less whine) at the slightly slower speeds.
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