You're welcome!
About xruns at play start: I'll refer you back to my first post on this thread.
Also you can try adding another block, to see if those xruns go away (64 x3). Or try 128 x2 (or x3). You may find a setting that works with no xruns at all, at least unless you do something very CPU-intensive. I use 3 blocks of 128 samples and it's rock solid unless the CPU is just about 100%. Or when loading a large drum sample bank I might get a single xrun (it doesn't affect me while I'm working).
I guess your FW device is fine, after seeing this result. It might take a bit of balancing to get it "perfect", or if you don't mind the fact you get xruns on playback start it's probably ok. There still might be a setting for "power management" of the FW device, "throttling" it when you don't want it throttled. (If it has to "throttle up" when audio playback starts for instance, that could be why you still get xruns.) So that would be something to search for.