Vandersteen 2w low output levels

I know my gear is at the low end for this board, but I've been unable to get any direction anywhere else and hope someone here can help. I have a Vandersteen 2W and a pair of Monitor Audio MA700G/MK2 bookshelf speakers. For many years this set up worked quite well for me. Recently, the 2W developed a loud ground hum. I can eliminate that by grounding the speaker to the amp. However, the apparent volume level of the 2W seems to be about half of what it should be. In other words, at any given volume level,the Monitors seem to be much louder than the sub.

I have tried multiple amps, changed the cables, changed the electric circuit and sent the 2W electronics back to Vandersteen - he says the 2W is fine and I have a ground loop issue...

For many years this set up worked well, but it is sonically intolerable,now.

Can anyone suggest a possible solution? Absent that, any recommendations for a similar setup -- I like Vandersteen's approach of filtering the bass frequencies out of the bookshelf units.

Thanks

ma700g/mk2