Soren,
I have the XA100.5. I used to have the XA160. In my system, Eggleston speakers 87dB/6ohm, the 160s were a little slow/heavy in the bass as you describe. The XA100.5 has much faster, more articulate and defined bass and are better balanced overall. Great control over the woofers. The mids on voice and strings are exceptionally involving - lots of body and presence. I have not heard the XA30.5 or XA60.5. Matching a pre to Pass amps is very important. I auditioned a very well regarded tube preamp which sounded terrible in the bass region with my amps but great in other systems.
