I understood that the DB7 was developed from the XJS platform rather than the XK8, and that the XK8 was then a development of the DB7 platform (rather than the other way around).
The DB9 is a cracking motor, and for what it is looks strikingly good value on the second hand market. A quick trawl turned up several nice, apparently well cared for Volantes with modest mileage in the £35-40K bracket.
Best of luck with the search.
