If I may throw in my 5¢
BOSE uses a thinner wire because their speakers are 2 ohm, whereas most aftermarket speakers are 4 ohm.
I would think it'd be far cheaper to replace your current speakers, rather than repairing them. Of course the trick is finding decent 2 ohm speakers. I call this plan B.
Plan C is to check on eBay for used speakers.
Q45 -1997-2001 Speaker Sizes
Front door: 6.5 inch
Rear door: 5.25 inch (These appear to be mounted in a bracket. Probably need the space for the window to roll down.)
Rear deck: 6.5 inch
DOOR TRIM Removal and Installation Details are on BT-28.