If it didnt knock before and now its knocking.. something has changed. You need to go through the systems on the car(fuel,alky,ignition) and see if something is now different. And try to refrain from hi-boost until all is well.
Had a customer a few weeks ago that the plastic tube going to the 3 bar had split on the bottom.. and when he went into boost.. the system would come on but now not deliver the correct amount becuase the MAP wasnt seeing full pressure.
My suggestion as easy rule of thumb is look at the alky tank, it should be going down. If it is.. more than likely the alky is working. The test button should work as it did when the system was first installed. If it does.. more than likely the alky is well.
You didnt put information as to O2 numbers. If theyre crashing.. or EGT coming up hard.. see what I mean
Point is with 20 year old cars... you have to be on top of them. And things like coil packs, ignition modules, fuel pumps(dont care if theyre new), fuel filters, engine mounts, etc.. can create knock issues.
Drop me some better data. And when you do your testing, try not doing it from a dig.. as too many things come to play. IE, manually put the car into second gear, bring the rpms up to 3-3.5K.. roll into the pedal.. and watch the knock/O2's as the boost comes up. Slamming the pedal down all of a sudden.. never know what ya gets
HTH