Hi, I think I may stop short of changing drive units as I'm not sure if these Audiomaster speakers are keepers. I bought them to see if I could improve on a pair of Monitor Audio MA4 Mk1's and I must say these are proving hard to beat as they have a lovely warm sound and very smooth top end (which I highly value). I may well try to find a new home for the Audiomasters, nice though they are. Strange though that the mid 70's MA designs seem largely overlooked these days, whereas the likes of Spendor BC1 and Rogers Studio Ones are venerated and worth approximately nearly 10 times what I paid for my MA4's. Would be interesting to do a direct comparison, but I suspect the MA4 would not be too far behind. Must be the kudos of the BBC affiliation of Spendor and Rogers. Apparently theMA4 Mk2's use the same Audax tweeter as these Audiomasters and sound worse for it. Not the best looking speaker in the world though, the old MA4's, it must be said!