Complex sentence: In 1990 the OA 401 watt 50 stereo amplifiers and the OA 601 watt 60 were added to the range, both amplifiers gained a solid reputation due to their technical features, sound quality and high power.
Split into simpler sentences: In 1990 the OA-401 watt 50 and the OA-601 watt 60 stereo amplifiers were added to the product range. Both amplifiers gained a solid reputation due to their technical features, sound quality and high power.