Nolas flat? No life?!? Not the Nolas I've known and loved, and that includes 6 different models, including the Contenders. BUT.
The earlier Contenders and the newer Contenders sound as though the tweeter is voiced differently. The earlier ones were brighter-sounding, something that, if you read John Atkinson's measurements in Stereophile when they reviewed them, is clear. He found a slight brightness around 9kHz: That would certainly give more life to the sound if not matched with something else bright. I remember playing the Supremes Anthology album when the first pair I bought arrived: for the only time in my (audio) life, I could not listen to that album. Bright??? No, it was BRIGHT!!! As it turns out, listening to the album 14 months later, it was the combination of the Nolas and the new Nordost Frey 2 that caused this effect, but even after the Nordost fully broke in (nearly 30 days later [no exaggeration], the Contenders had a heightened treble, evident if you listened to any Ella Fitzgerald CDs, where every single breath she took was audible - easily audible at that.
The newer Conteders are more balanced in the treble, but are "quieter" with solid state than with tubes (and Nola never, EVER shows at shows with solid state. ONLY tubes).
But flat, as in two dimensional? That's not Nola's "sound." They - all the models ever reviewed (and, again, I own six different models) - are all fully three dimensional with outstanding low-level detail. I don't know what was going on there, but it wasn't the speakers problem. I can get mine to sound "flat," but only due to placement in the room.