The best replacement for mtx is kicker.

The best alternatives to mtx are rated as following:
★★★★★  kicker
★★★★★  rockford fosgate
★★★★  alpine
★★★  jl audio
★★  jl
★★  kenwood
★  infinity
★  2tx
★  rockford
★  kicker subs
★  hifonics
★  btx
★  kicker subwoofers
  sony xplod
  audiobahn
  atx
  jl w7

Your alternative for mtx is not listed? Suggest!
Speaking about mtx, one probably shouldn't forget about mechwarrior 4.

Other search terms related to mtx and their ratings are:
★★★★★ mechwarrior 4
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Google Trends

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mtx
kicker
rockford fosgate