Yes, the A5.5 is good - lots of power to take control of woofers and air in the Hawk cabinets. I have heard it's precursor the A5 with some small B&W floor standers and some Revel stand mounts and it was wonderful in both cases. I have heard the A3.5 with Totem Arro's and it was outstanding - so am thinking the A5.5 might be the ticket with the Hawks, but haven't heard that particular combination.
I have heard the Naim Nait 5i with the Hawks and it was very good, but was actually a better match for the larger Forest (actually a match made in Heaven!). The Nait XS is a little more powerful and MUCH more refined than the Nait 5i - so am thinking it might make the Hawks really sing...
I think the Plinius will be warmer than the Bryson FWIW. Read about here:
http://www.positive-feedback.com/Issue19/plinius9100.htm