Second adapter worked better. ARC done. Still not impressed with the "don't include the adapter in the box approach tho. The Serial cable they include looks like it's a high quality piece - geezus... grrr....
Now - back to results.
Didn't notice a huge difference with ARC on 2 ch music, a little more pronounced bass, not too much otherwise at low to medium volume.
For DD from my sat box, sound is good, centre is a little more pronounced but not in a bad way, just tends to draw the attention back to the screen.
Will try to post the graphs later
Anthem AVM60, Totem M1sig, bi-wired with Bryston 4BSSTs, M1Sig centre, Mites SB, Sur., Paradigm P80R heights. 2X Anthem MCA-50s, Paradigm PW2200 sub. APC J15