Just to clarify, inkjet OEM printer drivers manage color in RGB while most inkjet RIPs manage color in CMYK. So the use of driver or RIP dictates your color mode usage for color management. Clearly, these printers are neither RGB nor CMYK, and the final 6-12 multicolor conversion is performed on the printer's processor on the fly while printing.
Your working space should be large enough to cover the gamut of your final printing process. sRGB is likely to be too small, while AdobeRGB and ProPhotoRGB are probably better choices.
As always, there should be a strong focus on determining the optimal paper choice for your needs and acquiring an excellent profile for it.