Need Dac/Amp recommendations

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I'm currently running a 2.1 setup for my pc using the Denon avr-3805 with rti4s and a psw505.

I'm a newb at this game and would like to know if I would benefit from a dac/amp combo or a 2.1 integrated amplifier setup instead?

Also, should I upgrade the rti4s to a rti6s or rtia3s or any other recommendations for a bigger soundstage?