jimmy im only posting on the 840a results, but with the ms mezzo2's and 6's i listen to the main faults with the 640a was at low volume i found they were a little bit light at the bottom end and i found i kept hearing one channel over another almost like the balance was not right until you got to the 8-9oclock on the volume. i even checked 2 640a amps as i thought it could of been a faulty one. and loud volumes the midrange seemed a little forward wear the 840 had great control but was still a forward listen and a touch pricey back then at £850.
plus i knows its no way to but a product but the 740 does look a fair bit sexier than the 640