I may get corrected but I'm pretty sure HDMI will NOT improve your sound. It's cabling, and improves the picture more than the sound. Adding sound is a convenience.
So long as your source has digital out (coax or optical) to connect the sound to your DSP-A1 you will get HD audio. And a $600 receiver will be a material downgrade from your yamaha.
So long as your source has digital out (coax or optical) to connect the sound to your DSP-A1 you will get HD audio. And a $600 receiver will be a material downgrade from your yamaha.