Always best to listen to an amp/speaker combo before making a decision, but you knew that. I like the old Threshold products (especially the SA series). I would not consider moving to a ML amp (except the old ML 2) anything but a lateral move. But that is just my humble opinion.
Now to something more pratical. Both amps are approaching the time when they will need to be re-capped (if not already done). Check out who would do this and how much it will cost.
Personally, I'd pass on the opportunity to get the ML and wait until you get new speakers. Who knows, your next speakers might be happy with 25wts or less and the sweetest SS amps aren't necessarily the highest powered ones, just the most expensive. :-)
Now to something more pratical. Both amps are approaching the time when they will need to be re-capped (if not already done). Check out who would do this and how much it will cost.
Personally, I'd pass on the opportunity to get the ML and wait until you get new speakers. Who knows, your next speakers might be happy with 25wts or less and the sweetest SS amps aren't necessarily the highest powered ones, just the most expensive. :-)