either way? An upgrade on either side, provided it is of sufficient quality, will be an improvement. The amp by itself, as an amp, is gold.
But it is not a simple case. For me the greatest increase was by adding battery power supply to the amp. FAR and away the biggest upgrade.
Equally an upgrade was adding the battery powered warpspeed LDR.
Have yet to try a high end dac, but my XDA-1 was nice.