I had an Aurender A10 with the built in DAC and it was not as good as the built in DAC in my Mac C2700 ( DAC2 board) in my opinion anyway. The Aurender DAC was dry and rather boring sounding, the only thing I found it exceled at was it had a very low noise floor. The MAC DAC 2 board is really good for the money, but most DAC's above $2500 will out perform it. You can put a DAC2 board in your current C53 I believe. The HDMI ARC connection is great if you have a TV in the same room so that may be a factor.
That said I got a Chord TT2 to try and it blew the DAC2 board away in all regards, I now have a Chord Dave i got used and its even better.
So a DAC is probably the best way to go IMO.