The orginal question can be paraphrased as; "which
board is better" (see the subject line).
Tim S. couched his replies in the form of an ATM only
solution. I feel that the HSSI board was not designed
as such. Your comments seem to back up my assertions.
I would claim that for raw throughput, and assuming
the DS3 daughtercard for the AIP, that the HSSI board
delivers more useful bits at the expense of an outboard
CSU. This is based on my feeling that HDLC is more efficent
than ATM signaling/framing.
Agreed...
But it's not a feeling, it's a fact 
--bill
Avi