Storage Is 15TB RAID5 with different controllers possible?

I would like to build new htpc/server for myself, and I'm going to use Zotac H67ITX-C-E or Zotac Z68ITX-B-E motherboard with Lian Li PC-Q08B case. The case itself has space for 6 3.5" hard drives, 1 2.5" hdd, and 1 5.25" cd/dvd/blu-ray ROM. Therefore I would need 8 SATA ports available, 1 for DVD, 1 for 2.5" HDD with OS (Windows Home Sever 2011 or Windows 7 Ultimate), and 6 ports to put 3TB HDD on each, for 15TB RAID5 array. Both of those motherboard have 2 6Gbps SATA III ports, and and 2 or 4 3Gbps SATA II ports.

My question is, they probably use a different controllers for the different ports, but does that matter? Can I put a HDD on a SATA III port on Marvel controller and 1 HDD on SATA II port on Intel and make RAID with it? In addition, since the ports are not enough, I will buy RAID controller like this one: MODEL# IXBAY-PX237

http://cgi.ebay.com/PCI-E-SATA-x-5-...389?pt=LH_DefaultDomain_0&hash=item5d2e258915

Would that work? Or for RAID I need all the ports to be from 1 controller? Keep in mind, all of the controllers support RAID5. This controller here has only 5 internal, and 1 external port, so I cant use it alone to connect 6HDD on it. Can I use the 5 from here, and 1 from the motherboard, to connect 6 3TB hard drives, to create my 15TB RAID5 array? IF not, please give me some solution.

Thanks.