I've read some reviews that suggests that their quality is a bit lower. The ripples are a little bigger (which is NOT a good thing), and also you get modular (i.e. removable) cables with the HX/AX series.
Additionally, the TX series power rating is a maximum power (i.e. delivers UP TO XXX Watts), whereas the HX/AX series use a continuous power rating (i.e. delivers XXX Watts when running normally).
The HX and AX PSUs are built by Seasonic, which is probably the best PSU manufacturer in the world. Another good PSU built by Seasonic is the XFX Black Edition (comes in 750 and 850 models), and is a little cheaper than the Corsairs.
I don't think that corsair psus are worth it for 750w-1000w which would be the amount you need to run CF/SLI I would rather go for the xfx 850w be http://www.newegg.com/Product/Product.aspx?Item=N82E168... very high quality, made by seasonic, and is much cheaper than the corsair equivalent, the 850hx.
The only TX i would purchase is the 650TX and I would only use it for single-card systems, I know boiler runs dual 470s off a 650w but you have more headroom with an 850w.