Music Streamer II DAC nasty issue. HELP!

Well, just got a HRT music streamerII USB DAC after some sparkling reviews but I'm having huge issues with it, any thoughts or help greatly appreciated.

Here is the problem, first I tried the dac with a couple of cheap second hifis, it installed smoothly and sounded promising, even a pair of £13.99 trust pc speakers sounded better... then I tried plugging it into my main system (a Cyrus 6vs2 amplifier) and all hell broke loose [] It was fine for a few seconds, then the volume dropped out..then kicked back in at half... then it seemed to kick in FULL, making a noise that had me diving for the power off button and fearing for my speakers.

Tried it with different channels and leads and even computers.. always the same when I try it with the Cyrus, the volume control on the amp intermittently stops even working!.. if i turn it up and down it goes nuts.. kicking in FULL volume then out. I'm almost certain the amp is not at fault, as it works fine with dozens of other line level sources.

I note that the cyrus 6vs2 has a digital volume control at the pre-amp stage... it seems to me this might be the problem. I see that the full scale output of the DAC is rated at 2.25 volts, I'm no engineer but is that not a bit high given that most CD players give 2v?, I tried lowering the attenuation built into the amp inputs but that didn't help just did the same but quiter, my working theory is that it's simply too much juice for the pre-amp digital volume control in the Cyrus 6vs2.

Any thoughts??... I would hate for this problem to be unsolvable as I really like what Ive seen and heard so far except for this huge issue with the cyrus.