Luc, first a point of terminology: the DAC in your Yamaha is just as "dedicated" in doing digital to analog conversion as is a separate DAC. The separate one may or may not measure slightly better, but DACs in quality equipment such as your Yamaha already are doing the job with audible precision and no audible benefits are to be found in buying a separate unit.
As to the amplification, since you already have enough for the loudness you need, there's nothing to be gained from buying still more which won't be used. There's no magic to be found in putting the amplification process in more boxes when it's already being done in an audibly transparent manner.
