Why would you go up to a 55w ballast and not stay with stock wattage? For what its worth the Hella projectors in our cars throw a ton of foreground and 55w is not going to be a huge upgrade IMO.
A fresh set of D2S bulbs and new replacement ballasts if you need it would be wiser IMO. Do you have pre or facelift E53? If facelift, its Hella Gen IV and those have integrated igniters.
I'd recommend the Morimotos for a price affordable replacement, you MAY need the canbus modules in line, I'm not sure.
Morimoto XB35 OEM HID D2S Ballasts xenon D2S D2R AMP Denso Matsushita Bosch Hella Ballast 3Five 5Five