On our wide format inkjets, the RIP being used has a spot color remapping feature.

Basically it has the abillity to override CM completely, and let the user control the actual amount of CMYKcm going to print for a particular spot color. It works very well for getting deep reds and blues.

That feature will only work on files with spot colors that are saved as CMYK mode EPS files.

No RGB, no PDF.

Within the same file, there are placed Photoshop images. I would like to keep those in RGB to take advantage of the greater gamut.

What would be the ideal combination of placed RGB Photoshop files placed within a CMYK Illustrator file saved as EPS?

The RIP does have the ability to set different rendering intents for CMYK and RGB vector elements, and CMYK and RGB raster elements.