Tube upgrades for Jolida 502B?


I realize this is something that has come up before, though in searching the archives I didn't come away with a clear path forward. My amp is completely stock and came equipped with Sovtek 6550s. Using it to drive Totem Forest speakers. I contacted Jolida. They recommend KT88s. Their reply is a bit unclear but they might be suggesting Electro Harmonix. They also indicate reliability issues with Chinese KT88s. Response Audio (Jolida dealer and modder) recommends Shuguang KT88s (Chinese). The Tube Store recommended JJ Tesla KT88s on the strength of their great imaging and deep bass (more bass being something I was looking for). I was initially leaning towards SED Winged "C" 6550s. Now I am a bit more confused. I'm curious about KT88 vs 6550 sonics and reliability differences. Thanks in advance to any one willing to take the time to share their experience and preferences.
128x128ghosthouse
thanks guys for the info. 120's will be going in. just one step closer to the promised audio land.
I have the 502Crc (the integrated version of this amp) and verified w/ Mike Allen at Jolida that it is okay to run 120s in it (& they sound great in mine).

B
I have Kt120's on my Jolida 502B for over a month now. So far no issues and I love the sound better than the stock 6550s.
I do wonder how long the 120s are supposed to last as I've been driving mine hard for about a year and they've stayed absolutely stable, unlike myself.
the 120's are not working as hard as 88's or 90's would be. and who said that this amp can be run in mono?? there is nothing in the manual about this. and if they can be run in mono, what is the speaker hookup. + to +, - to + ??