Cannot help you, sorry.
I wish I knew what E88 tubes Luxman uses (and Cayin 6sl7/6sn7 also) so when their branded tubes get old, I know what to get that sounds like them.
I bought a pair of 6SN7 or 6SL7's from Brent for my Cayin. Didn't like them even after break-in, returned them, tried another version (half the price), sounded wonderful just like the Cayin's, I paid the shipping, Brent gave me a refund for the cost difference. Just dumb luck, a different tube might have sounded 'better'.
I think 'preferred', not better) is my reality with tubes over the years.
I also found some original Cayin tubes on eBay (seller was using different tubes in his Cayin amp., bought them for the future.