Well, I hope we haven't confused you too much ryounglaw

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The choice is yours, stay with the 2309 which is probably powerful enough, but cannot connect to an external amp, or return it for another receiver that does have pre amp out jacks, for at least the front 2 or 3 channels.
Is that worth an extra $400

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If you ever go for a more powerful external amp in the future, look to at least double the power. Triple it if you can. I think someone else said this earlier in this thread. I had a Denon AVR-1800 with 70 wpc. After several years I added an external 2-channel amp with 200 wpc, and used the receiver to drive the center and rear channels. With about triple the power for the front left & right speakers, I could easily hear the difference. Used amps can be a very good deal. I recently got a newer receiver (also used) with plenty of bells & whistles, but I still use that same external amp for my main left & right speakers.
Good luck whatever you decide, and best wishes from all us experts here at AH

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