All of a sudden my Stylus CX6600 started putting horizontal yellow, magenta and blue bands (sometimes all the way down the page!) over top of any type of B&W copy or print I try to make. It even happens when I do a nozzle check. I've changed every color cartridge and I get the same results. I've never seen this and there is no troubleshooting topic that addresses this.

Try to perform a print head alignment.

The narrow pink line is coming from your magenta toner/drum cartridge. You may be able to open the from cover and look at the 4 toners. If you look at the magenta (like pink) cartridge, you might see the thin line on the drum surface.
The multicolored band that sometimes shows up on your prints is most likely the transfer belt unit. This is caused by an area of the belt that is not being cleaned very well. This probably tends to show up when you are running mutilple prints of a page.
So it looks like to may need to replace your magenta toner and look at getting a transfer belt unit.

You can see the reference on the cartridge itself.
Take it with you when you buy new ones.

Open top cover press the toner buttom on the top then close the cover, you'll hear the cartridge changing do that until it cycles to the cartridge you desire

Epson printers Will NOT print with any empty cartridge installed.(any Colour) replace the empty carts and you should be on your way

Do a printhead cleaning utiilty

directly hooking the printer to mac and windows computer are you getting bandings still? interesting issue... we will isolate it first by trying to hook printer directly to both computer, if its printing fine when directly connected, then there is something on the application or communication process. try printing a different document using same application when on the network and try printing from different application as well. update me afterwards..

change your magenta led it sounds like that may be faulty big job if not theat then its a new rip baord which is under the cover

have you tryed to update your drivers on the printer

You need inividual nozzle cleaning with cartridges out of the machine. take a look at www.fixyourownprinter.com also down load the Epson utility from www.ssclg.com