The HD621 takes the digital audio stream from HDMI and makes it available to the digital multi-channel inputs on your G68J. There is no digital to analog conversion in the player and no analog to digital conversion in the G68. The extra D/A and A/D steps contain pitfalls (rounding errors, jitter, etc.) which can degrade the signal. The A/D conversion in the G68 is of high quality; however, the A/D conversion in most Blu-ray players is not. The sound is only as good as its weakest link - in this case DAC in the player. Whether you can hear the difference is of course the question. I am inclined to believe you can. I think most would agree that avoiding the extra D/A and A/D conversions is the route to go for the highest quality audio. Nevertheless, the cost of the HD621 in relation to the G68J is somewhat high, so you have to make the call as to its ultimate value to you.

561, DSP5500s, DSP5000C, analog sides and rears