Once again, thanks to all who have responded. Taking the advice presented here, the Vic Firths have arrived and have made a WORLD of difference in my ability to actually hear the mixer output.
Yes, there was simply too much ambient sound from the kit itself with the non-isolating headphones.
My current mic set-up is somewhat less desirable so in addition to the Shures, I am going to get either a pair of
Lewitt LCT 040s or
AKG P170s. But have not quite settled on which condensers are better as I have not been able to find a direct A/B comparison on the YouTubes.
So, if y'all have suggestions for a sub-$250 pair of overheads, I am open to them.
Lastly, in the spirit of "no pics no gear" -
And because I did not include them in my OP -
Once again, thank you all for educating me as I progress.