From what I remember, the SKY+ Remote will work with the Avant (but will not turn it on!)
In order to get the Beo4 to work with SKY+, you'll need to see if a set-top box controller is fitted to the Avant. The easiest way is to look around the back and see if there's what looks like a headphone socket. This'll be near the SCART sockets.
Alternatively if you go into Menu then Sources see if the option of "Set-top box" is listed under AV2. If it is, then select it and press "GO" where you'll be shown a list of compatible boxes. If the "PACE SKY+" (or similar) is shown, then you're almost good to go.
If it only shows "SKY DIGITAL" then you'll need a software upgrade.
Once you've cleared the above hurdles (and assuming that it's worked as above) you'll need a remote lead (around £20-25 from a B&O Dealer) - this runs from the socket mentioned above to a small remote transmitter (that sticks on the front of the SKY+ box)
Sorry if that's a bit exhaustive - it is definitely worth doing though - works a treat on mine.