Please disregard my previous post on the total cost of ordering CSP750's from Bigfoot. I looked at my invoice and although they claim free shipping on their site that may only be within canada, they dinged me $20USD for shipping and insurance for 2 of them so that would make them about $51 ea. vs $45 ea. from DTEK. They did deliver promptly though so I can't complain.
You can get the hardware to connect them in series from any Home Depot, plumbing supply place etc. I have not heard the MCP650, but the CSP750's are exceedingly quiet and would be essentially inaudible inside a case. You can find the pressure volume curves for the CPS750 here
http://www.c-systems.ca/c_files/image16big.jpg
The MCP650 Curves are here
http://www.dangerden.com/images/pump...urve_1000w.jpg
I believe the MCP600 is the same as this
http://www.dtekcustoms.com/index.asp...rodID=138&HS=1
scroll down to find the curves.