Yea, I think I'll try ordering the AD797s to try them, shame they take so long to be delivered. Might also try to source some of the others you suggested if I can find them cheapish.
I've since had other people listen to the new sound from my Essence One and they have all agreed that there is far lass bass and punchiness, however they all mentioned that the soundstage improved and there was more details in the trebles. But overall the concessus was that the stock op amps sounded better.
I'd put them back in but not sure they will work as the legs got pretty bent when I took them out. They might work if I bend the legs back but I think one of the legs looks too damaged and I don't want to run the risk of blowing the E1