Thanks, Kevin & Nailbunny. Now that I know what to listen for, I'll concentrate on the bass and see if I can discern a difference. Very glad to know there isn't a "right" position.
After six weeks, it and the Omegas are still opening up!
Yep, in tube audio, there is seldom a 'correct' setting. The option that gives the most power often also produces the most distortion. Transformers that produce the widest frequency and support high power output almost always have more inductance, causing upper most frequencies to roll off a bit, same goes with when you use the 4 ohm output instead of the 8 ohm output on the transformer. Some people love the type of distortion single ended tube amps produce (since it's almost all even order harmonics) and some people don't like bright amps, but love tight bass.
The point is that everything has tradeoffs (though in many cases, these may be desirable). Happy listening
*Random unrelated piece of advice: Many people spring for expensive upgrades to their already great equipment, but it would almost always be better to get your listening room treated instead. It really makes a much bigger difference than things like capacitor upgrades, etc.