With "Direct Monitoring" on there should be zero latency (you're routing your input signals direct to your headphones without going via the computer) so something is clearly going on here.
The first thing I'd do is go to the Roland site and download/install their latest drivers.
Beyond that, I notice from the manual that the Direct Monitor Volume knob is doing more than the name implies. It's actually controlling the balance between signals coming from the computer and the stuff on the the direct input. I don't know Acoustica at all, but could you have a button selected so the "new" material is being routed back to the Edirol interface. If so, the effect of the Direct Monitor Volume knob would be to mix between zero latency and latency. Your best bet would be to turn off the monitor playback of the new tracks in Acoustica...might be as basic as hitting Mute on the tracks you're recording...but I'd hit the manual to see if there's a better way.
FYI, with the Direct Monitoring, none of the buffer size stuff etc. should come into play. However, if you use any MIDI then it all comes into play since MIDI must go via the computer.
Hope some of this helps a bit.
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