ARCAM: is it me or is it a bit compressed?

I would try a more powerful amp with that speaker, it is not particularly efficient. IMO it needs more power to open up, sounding great with some big krells the last time I heard it. The older, less efficient dynaudio speakers did sound compressed to me when auditioned using low to medium powered amplifiers, while the Special 25 to me has more dynamic ease with my Arcam integrated.

The 1.3SE's, and all of the Dynaudio line is not Biampable. Ugh

Biamping my AVR300 was a genuine revolation in the overall sound. Can't guarantee how it will impact your system, but you should consider getting ahold of some biwired speaker wires, if you don't already have them, and giving it a shot.

I have used the Arcam recievers (AVR 100 and 200) with various speakers. As good a component the Arcam is, it does have it's limitations. I had some difficulty with driving my Usher RW729 with my Arcams. Some speakers will need more amps to "open up" the speakers. The watt power may be sufficient but it may take more amps to "fill out" the sound. Once I used the Ushers with my Linar or Edge components the sound "opened" up.

have you tried bi-amping the speakers using the AVR300? Definitely adds more to the output