Due to lack of anything better to do right now, I took a look in the VX5500 service manual to see how they original "VX sensor" might work. I got bored searching for it or its connections in the circuit diagrams, but found a note that said the only thing special with it was the plug wiring, and a referral to the service manual on MCL 2 C, whatever that might be...? (couldn't find anything like that on site).
Anyway, the point in my babbling is that I believe it might be a very simple thing to implement nowadays with a IR receiver module capable of receiving the B&O carrier frequency (455 kHz, i.e a TSOP7000 - integrated circuits like these weren't available in those days, so the original receiving circuits were quite complex). But I'm afraid the dealers won't and frankly can't help with these things - all they could do is to sell the original sensor, which obviously is more than obsolete these days.
Edit: of course the sensor connector pin-out is on the first pages of the service manual. All it has is ground, +5.5V out and data in. I'm pretty sure it could accomodate a TSOP7000 either directly or after data inversion (meaning add a transistor and two resistors) - either way, this should be a less than 10 euro job (not including anything to make the sensor look pretty) and not require you to even open up the VX. I might try this one day as I have a VX5000 and all the rest, but please don't hold your breath...