Playing system essential to faster wagering theory (6)

I believe the answer is:

stereo

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'playing system' is the definition.
'stereo' can be an answer for 'system' (stereo system is a kind of system). I'm not certain of the 'playing' bit.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for stereo that I've seen before include "Method of sound reproduction" , "With twin audio channels" , "System of sound reproduction" , "Sound - not mono" , "Matched, rivalled" .)

I've seen this clue in The Irish Times.

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