Not sure how different the D6 would be but I am sure it will be similar....
I had a quote for my KAD44 from a proper Volvo agent - winterise, service (filters, oils, anodes and outdrive) and de-winterise - £1300!
I decided to do it myself for £250 for the parts. Not only that, but I could get the parts (genuine Volvo) cheaper from one of the places in the back of the magazines than he was going to charge "at cost"!!
Just be careful you are not violating any warranty by not having it done within the Volvo network.
The prices authorised agents charge is just unbelievable.