My logic is because I was figuring the port would override the card in slot 6, but the procedure described will work. (I'm not as familiar with the IIGS as I'd like to be so I was unaware of that).

I suggested an alternate slot because I did that on a IIe once when I set up two floppy controllers (one for UniDisks/DuoDisks and the other for a Disk II). I had one of one drive and one of the other. I think I put one of them in slot 5 and used that as the second drive (which meant a lot of configuration on my part).