The SV6, and SS Head units are very similar to the Omega unit, with the exception that the CD Stacker supports MP3s, and has more Wattage...
The Berlina is the next step up from that, and has a large single colour LCD screen, and support Dual Zone Climate control..
The Next step up is the SS-V / Calais Head units, which have a colour LCD screen, supports composite video input (Such as reverse camera, roof mounted DVD player),
Supports the factory Sat-Nav system by displaying map information, supports Dual Zone Climate Control, and supports Park assist (Displays object distances on the display)...
The SS-V, Calais Units are the way to go if you want to retain a stock setup. (I.E. no iPad, Andriod, in car PC system)..
There are a couple of threads here discussing what is required if you wanted to fit a SS-V / Calais (Colour LCD Radio HVAC Head unit)...
It basically requires some EEPROM programming, and some wiring (or fudging of wiring)...
This page shows the Calais Head unit, and the EEPROM programming proceedures...
www.carmodder.com • Programming the Colour LCD HVAC / Radio for the Holden VE Commodore
Hope this helps...