I have the opportunity to use a few wide format printers, mainly Epson, possibly Canon, on Weds, this week.
Ray,
I am reading your post and trying to decipher whether you have access to print on these printers, or have someone make prints on their printers.
If you are going to print to these printers, simply set your print size to the size you like, (depends on available paper etc) and print.
All the upsampling interpolation will be done by Hybrid SE as you make the print.
There is no point to upsampling an image to 300 ppi before you print.
If you are going to be using someone else's printer, then I suggest you carry a Qimage install file on a thumb drive, and install it on their computer, and follow the directions above.
You would not have to carry TIF files either, Raw or Jpg would work fine.
You can use print to file, and set that to 180 ppi at various sizes, and present those for him to print using his equipment.
If it was me, I'd make him print one using Qimage, and then see if he can match it.
Fred