Heads
No you can't.. and don't let the dude that sells these on Ebay fool you either, his $100+ "dual" feed consisted of a home-brewed pump set which if it breaks your not going to be able to obtain anywhere but from him if he's still around and a pump which has no commercial support in the US.
I know, I bought one and returned it. And if I haven't mentioned it before, I chose the Kangaroo 324 because I know that it was and still is in wide-spread use in the US. (I'm not just a web hosting provider/jack-of-all-trades/fish freak.. I'm also an RN). Meaning you can easily get pump sets and you could, if they weren't so cheap, even get the unit repaired if desired.
As to pumping equal volumes, what I find is that you typically end up pumping one part at one rate and another at another based upon usage and testing and, if you making your own 2 part, based upon the concentration of the solutions as well as the other parameters.
For example, I'm using two pumps right now, one is going at 18 the other at 22.
When I get the 210's setup (I hate plumbing) I'm actually going to pump three parts; Alk, Calcium and Magnesium.
And one other "small" issue, the ALK solution, even mixed at half-strength, ends up clogging the pump set on average about once a month. I "clean it out" by flushing the pump set with vinegar. In my opinion another reason to use seperate pumps.
Regards
Noel