I wrote Apeks UK and here is the response I received.
Dear Chris,
The ATX100 won't be available in the States, the distributor has decided not
to take it, but we are expecting the ATX regs to quickly supersede the TX
range, although we are still running both lines. The ATX range have a
smaller 2nd stage with more adjustment to give ideal breathing
characteristics and ATX200 has a new 1st stage in black chrome, which you
have seen.
You can contact Aqualung America for more details on the range available in
the States.
tphillipp@AQUALUNG.com
Regards
Landon Helsby
Technical Service Manager