Areca have provided the source code for their Solaris driver, including support for the newer 6G RAID adapters. As a result, I've integrated a (somewhat cleaned up) copy this code as an update to arcmsr(7d) in illumos, under generous open source licensing:
user: Garrett D'Amore
date: Fri Mar 25 22:14:56 2011 -0700
834 need support for Areca 1880 6Gbps
Reviewed by: Dan McDonald <email@example.com>
Reviewed by: Albert Lee <firstname.lastname@example.org>
Reviewed by: Richard Lowe <email@example.com>
This will make another HBA option available to folks. (Note these cards do support a JBOD mode, so you don't have to use hardware RAID -- indeed I would recommend that you don't when you have ZFS on the disks.