Somehow got Jplay Femto to play at the highest setting (1000). Not sure how I did since I made a lot of tweaks since the last time I tried. I basically gave up on ever getting it to play at that setting. Perhaps it was changing the XMOS buffer settings. At any rate it's working now and man, so good.
And this is with a cheap cheap dac. Just goes to show there is so much performance left on the table with PCs/software. Frustrating at times, but when it pays off...