OK so i'm very new to the navigation units. i have quite a bit of stereo knowlegde but have never delt with nav units. I was given a AVIC-90dvd unit with an AVD-W6010 display monitor. I have NO NAV DISC. I know it came with a cndv-20 which was upgraded to CNDV-21, which i heard was surpassed by a CNDV-40MT. Now i heard that a CNDV-50MT will work. I am so confused and don't want to get something that won't work with my application, since i am using a remote not touchscreen. Please if anyone can tell me which discs will work for me i would appreciate it.