I commented on that thread and as others said probably not being driven well enough , as what you were hearing was definitely not what I’m hearing from my Diana TC’s.
I’m glad you didn’t give up on them as I listen to them much more than the other headphones I have and with the new bass ported pads gives them some added bass punch and also widens the soundstage a bit. I have not heard the Omega Lupi and 250 mW does seem a bit low but my Amps and Sound Kenzie only does 350 mW @ 32 ohms and the TC’s do sound fantastic with it as well. A lot of my listening is done thru my iFi iDSD Diablo as I like to sit out on the back patio with a brew or a bourbon or two when the weather is not too inhospitable.