@dsper
As you likely know very well, a McCormack DNA-500 is no slouch, quality build, big transformer, 500 watts, a capable amp - originally $7k retail as I recall.
+1 on 8ohm speaker impedance comments shared above in your favor.
If I were in your shoes, having come from similar SS amps over multiple decades, and gone through multiple stereo tube amps, I'd recommend demoing at least equivalent cost or higher quality level tube amps compared to your DNA-500. Otherwise you might end up disappointed and not really gain a proper perspective of the potential difference.
Perhaps some nice mono tube amps with quality made [beefy sized] transformers that don't break a sweat [nor run hot] might grab your attention, and for your low level listening requirements.
Many folks here can suggest a few good ones for consideration! :)