that sounds peculiar,,,,,, I happen to own a DL-103,usual disclaimers apply if you use a 103 "R". anyways I have used both the Denon AU-300 as well as a pair of Altec Peerless 4722 mic trannies,configured (with a toggle switch)for both a 38 ohm load as well as a 150 ohm load and while the Denon unit functioned well.... the Altec 4722's were head and shoulders above that, the whole audio spectrum is more "FLESHED OUT" and elaborate! nothing jumped out of place everything was just continuous more of a GOOD thing if you will...you have to experience it for yourself... as Leman said "...significant improvements in detail and soundstage" HUGE improvements. And I'm sure some will say these don't even compare to the Custom jobs that Jeffrey Jackson makes...
you should consider, these babies can be had for < $300