......and sexual innuendos aside

, as I understand it the main differences between the Discover Media and Nav Pro are:
Discover Media5.8" Touch Screen with 400x 240 Pixel Resolution
2D/2.5D map navigation (Europe) with voice control
CD drive MP3/WMA
Music playback from MP3, WMA, AAC files with title display from SD and AUX IN
USB, AUX-IN, SD (2x) (Aux and USB require optional connection cable) - only 1 SD card available for music, other SD card contains Map data
DAB, FM and AM radio reception
4x20 watt output (front and rear speakers)
Bluetooth connection for phone and media (HFP, A2DP *, AVRCP **)
Discover Nav Pro8.0" touchscreen colour display with 800 x 480 Resolution
Faster 3d Display Engine (graphics Chip)
3D map navigation (Europe) with advanced voice control
DVD Audio/Video
Film playback from AVI, MPEG, Divx, H.246, and DVD from SD, USB and DVD data carriers
Music playback from MP3, WMA, AAC files with title display from SD and AUX IN
Gracenote database, podcast playback and jukebox
Internal 64GB memory as SSD - (Solid State Hard Drive) - 30GB can be used for music, etc.
USB, AUX-IN, SD (2x) - both SD cards available at all times (maps are stored on the HDD)
DAB, FM and AM radio reception
4x20 watt output (front and rear speakers)
Bluetooth connection for phone and media (HFP, A2DP *, AVRCP **)