Try calling Yama's and tell them the cable on your Lambda is foobar. I'm guessing though that it would be cheaper to get a SRE-725 extension cable instead.
Yes, to some degree at least. The bias is the potential of the drivers so smaller drive voltages are needed but they will still be a tricky load so current is again the name of the game here.
I'm sure they were being a bit conservative so a 400v+ bias voltage could work. The bias is governed by the square of the D/S gap so if the gap is 0.4mm then 500v would work. A SR-007 works just fine at 750v...