The P600 will have to be flushed out.
The P400 can use a set of 60ml bottles and get 4 fills from them. The P600 could as well... and get two charges of ink.
The P400 you would need to swap two cartridges to go between MK and PK. The P600 performs black ink changes.
Both do 13" wide.
I think that the P400 PiezoPro system can be had for a set of $240 inks:
and a set of refillable $46 cartridges:
The QTR software is $50, PrintTool is required if you are on OSX.
Piezography Professional Edition Toolset is not a requirement, but it sure is an awesome set of tools that do quite a bit.
Certainly - your entry into the P400 is cost of printer and only $286 for the Piezography Pro system. With the current $100 rebate from Epson the printer is only $500. So I see $786 getting you into the Pro system... plus QTR and Print Tool if you do not currently own them.
The P600 adds quite a bit more in terms of requiring to flush out the color inks from the ink line, ink exchager, etc.. and that requires a set of carts...
You're not giving up much by having to swap the PK and MK carts when you wish to print glossy or matte.
Hope that makes sense....
Best,
Jon