I have a laptop with an SSD and an older spinning HD from a previous laptop that I put into an empty bay. GRUB 2, installed onto the SSD alongside Win 10, didn't have any problems detecting the existing Linux installations on the added spinning drive and adding them to the boot menu, so I think you're going to be fine, barring any whacky UEFI issues that may be specific to your machine.
The MX Linux repositories
: Backports galore! If we don't have something, just ask and we'll try--we like challenges. New packages: AzPainter 2.0.4, Pale Moon 27.2.1, Liquorix kernel 4.10-2, mpv 0.25.0, Kodi 17.1, Ksnip 1.3.1, Mesa 13.0.6