I've never owned a 9300, but I do own a 8500, and have also owned a 9000 like you. I did once look into getting a 9300 myself but decided against it as I was told that the amplifier was not as good as in the 8500 (and I use my 8500 with passive Beovox speakers, so the amp is important!). When I researched the 9300 however, my understanding was that the Phono and Tape 2 input buttons would work dependent on what was connected to that input - if you had the Beogram 4500 connected to it, you would be able to control that by remote, and likewise if you had a B&O external tape deck connected instead. One way to extend the inputs would be to add a B&O MCL2AV link room system which you would connect to the Aux input of the 9300.  You could then connect your internet box and REVOX tapecorder to that, and switch to them using LINK room commands on your B&O remote.  You could have your Beogram 4500 connected to the 9300's Tape2/Phono input, which would have the advantage of allowing you to control the Beogram with remote too.