The best replacement for 4 channel amp is 2 channel amp.

The best alternatives to 4 channel amp are rated as following:
★★★★★  2 channel amp
★★  5 channel amp
★★  monoblock
★  mono amp
★  2 channel
  6 channel

Your alternative for 4 channel amp is not listed? Suggest!
Speaking about 4 channel amp, one probably shouldn't forget about 6 speakers.

Other search terms related to 4 channel amp and their ratings are:
★★★★★ 6 speakers
★ 5 speakers
You have in mind a companion for 4 channel amp and it is not yet here? Propose!



Google Trends

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4 channel amp
2 channel amp
5 channel amp