That's a sound expansion upgrade (like sound packs for Yamaha's, sampled expansion sounds for Korg's etc., ALL of which cost money!) as well as an OS revision.
From a post by you a few years ago:
The instrument is OAS 7 ready, and the current upgrade cost is approx £370 plus fitting (The upgrade has to be performed by a Wersi Engineer, and has the added advantage that a 12 month warrantee is automatically supplied)
Full post is here:
http://leighwilbraham.forumchitchat.com/post/Wersi-Abacus-OAS-6-2036451 How much
have you put into your Abacus over the years, Bill? LOL
There is considerable totally new stuff and a lot of older features not included in the original OS for the BK-9, all completely free. Roland do a great job of extending the lifespan of their arrangers (they brought out an OS3 for G70 two YEARS after it was introduced!) at no cost.
There is a feature not yet implemented for the BK-9 where you WILL be able to add additional sounds (new samples) to the internal ROM, and that (like the Atelier update)
will be a paid for addition. But OS upgrades have always been free for the arrangers, AFAIK.