Dilly, the Lowther drivers don't really have a limited life span, it's just the cone/suspension surround which will degrade over time, just like any other driver. Lowthers use a foam type suspension surround, which probably lasts about 12 years or so. When it starts to go bad, you can just get them redone by the factory.
I can't comment on the particulars of those two amps you are considering.
I can't comment on the particulars of those two amps you are considering.