Ed,
No, it is not just a warmup issue. Yes, I forgot to list, as one of the negatives, that the phones do take some time to warm up. But, even if I leave them playing for some time before I start my listening, I hear that coloration. I am aware of it all the time, but I acclimate to that sound. It is the same when I visit friends and hear their speaker systems. All have characteristic colorations, and I usually can tune them out. The somewhat "dry" (leanness) sound that leaves me feeling a bit cold listening to the Stax is actually a bigger issue. That I find a bit harder to tune out, though I've heard my phones sound completely free of that problem (through a ridiculously expensive Kondo M-10 linestage), so I suppose it is not really a characteristic of the phones, but, their extremely demanding nature (they reveal everything upstream).
I am being hypercritical, because that is what the original poster asked, but, I am still quite pleased with the Stax.
Spritzer,
You state that the 007-t is underpowered. That, I cannot disagree with. But, HeadAmp specifies 54 db of gain for the BHSE, which is the same gain specified for the 007-t. Can you elaborate on how the BHSE delivers more power?