Hi Tharshan
If you’re gigging I would recommend the Ikarus as it has 76 Notes and an all aluminium case to reduce weight.
The Abacus is heavier (Built like a Tank) but can easily be expanded to an organ if required. (76 note lower manual, 13 to 25 Note Pedal board)
Like most European manufactures (Including Korg) the keybeds used are made by Fatar.
The sounds you heard on the DVD were of OAS 6 which was released in 2004, all the latest instruments have OAS 7 (Earlier instruments can be upgraded, even the first ones that were released in 2000) which gives a major update in sound quality and versatility, (Particularly the internal voices) and also makes it even easier to use VSTs.
For more details of the OAS systems you can download a magazine here,
http://www.worldofoas.co.uk/sample.htm although please bare in mind that there have been many additions since the magazine was released.
The New Open Art Arranger Software is also due out this week, (Another Major Update) which among others allows Direct Play of all Yamaha Styles.
Wersi will be pushing forward their OAS system in 2007, with expansion of their overseas dealerships, however I think the closet to you at present is in the USA, you can check with them at
www.wersimusic.com or Germany direct
www.wersi.de Hope this helps
Bill