Rogue Audio Cronus tubes ??

My wonderful amplifier is approaching its "second birthday" at the end of the year, and I know I'll soon need to consider replacing the original Svetlana EL-34's. What have you guys used ? I love the sound of the amp just as it is, but I wouldn't mind "improved sound" if it can be had by using different power tubes.
No one must own any Rogue on this site. I asked the same question about a Metis pre-amp and got no responses. For what it's worth, I have a rebuilt ST-70 that uses EL-34's. I've tried the winged SED " C "s and NOS Siemens. I like them both, the winged "c" being a little more tubey sounding. The Siemens have a more neutral sound with more extended highs and bass.
Adam, I have the Cronus but with the Magnum upgrade so I'm using the EH KT90s so can't help with the EL34 but saw in one older thread that someone was using Sed Winged C's in his Cronus - why not give Mark O'Brien a call and ask him what other EL34s they'd suggest considering.

Would suggest that if you are using the newstock 12ax7s and 12 au7s thatcame with the amp switching them out for some Sylvanias, or Siemens Tungsol combo - can getthem a decent prices and they make a big difference
I am using SED Winged C with my Cronus with great result. Also, I changed the small tubes to NOS.
Back in May, under the guidance of Mark and Nick at Rogue Audio, I swapped out the five small tubes in my Cronus as follows :
an RCA NOS 5814 to replace the EH 12AU7 gain stage tube, a pair of GE NOS Five Star 5751 "goldpins" to replace the Sovtek 12AX7 input tubes, and a pair of GE NOS 12AU7A's to replace the EH 12AU7 driver tubes. Definite improvement !! I'm not sure how to describe it, other than saying the music simply sounds better.

So, when the time arises to replace the EL-34's, I'll obviously seek the guidance of Mark and Nick once again. The purpose of this thread is just to learn what you guys have done and to perhaps stimulate some nice conversation. Thanks to all, and Happy Listening.
Electroharmonix EL34EH worked wonderfully for me and gave additional improvement after I had converted all the small tubes to NOS Amperex and Telefunken.
I bought my Cronus from an Audiogoner and it had been modded (basically the Magnum upgrade before Mark and Nick gave it an official name).
When I got it the stock EL34 had been replaced with KT77s. The KT77s recently passed and I replaced them with EH KT-90s from BOI AudioWorks. I think they sound fantastic! Very punchy and detailed compared to the EL34s.