Has anyone, or can it be done, replace the standard audio unit in the GS model to the unit that is used in teh XS/HSE (IE. THe Hi-ICE audio unit? I was thinking about replacing this unit with the unit from a salvage Freelander 2 XS.

It's a complex project as the Hi-Line has much more components and communicates between them through a MOST (media oriented system transport) optical bus.
You need to install that optical network cables and others standard ones too because the standard unit drives the speakers directly while the hi-line has an audio amplifier in the booth.

Sounds like the easier option is to get the salvaged XS and put all the working bits from the GS on it  2002 Honda VFR800
2002 Toyota Celica 140 Silver (mid life crisis - again!)
2007 FL2 GS Manual Army Reconnaissance Green + freel2.com sticker
2004 Toyota Celica 140 Black - Gone
2000 Toyota Celica 140 Silver - Gone
1998 Toyota Celica ST Pearl Green - Gone
1996 Nissan Primera 1.6 - Gone
1994 Rover Montego 1.6 Auto - Gone

Thanks Alex.

Would you say its worth it then? I would like to update the audio unit as it only has the 6 speakers and prefer a good surround when im driving and i have jsut had a call from a salvage yard who have a HSE and are willing to take the audio unit plus speakers out for me for a decent price.

Or would it be best to get something else ( i am reluctant to do this as it would lose the feel of being a Land Rover)

The degree of "worth" is proportional with your desire...
Here are some additional informations: https://www.freel2.com/gallery/albums/user...ystems.pdf