The 1st F1 Digital+ broadcast was the 1996 German Gp, However I'd read in the past that they did a full system trial at Silverstone which was never broadcast.
In 2007 Premiere (Now Sky Deutschland) broadcast a short highlight program for Silverstone 1996 as part of there Die Besten Gp series & it seems to be using the footage shot during the F1 Digital+ full trial.
For the 1st 4-5 laps the TV pictures are the same as what was shown on the World-feed (Produced by BBC at the time) but the graphics are handled differently, Then from lap 5 on they start using some of there own trackside camera angles, A few of which would remain FOM angles going forward.
I put together a video running from the start of the race to the time Premiere's highlights cut forward a few laps to show the differences. World-feed via EuroSport is in the PIP window & what seems to be the F1 Digital+ trial footage is full-screen: http://www.dailymotion.com/video/x1ev8mw_1996-silverstone-f1-digital-test-vs-world-feed_auto