What kinds of tubes I can use?

I have no idea of the quality of your amp, but- As I stated at the end of my other post; there are numerous things on which good sound staging depends. To be blunt; Coming from China(or anywhere. China just makes it more likely), your amp COULD contain some really lousy parts that represent a disparity from channel to channel, or simply that will not cleanly pass ambience info. Cheap output transformers, or a poorly designed power supply, can drastically/negatively affect sound staging. The World's best tubes won't make a sow's ear into a silk purse, though they COULD make it somewhat more pleasant to listen to. I didn't mention a high quality source(arm/cartridge/table or CDP), preamp, interconnects, speaker cables and vinyl or CDs that were recorded/engineered/pressed well are all very necessary. A serious mismatch in any of the tube pairs that your amp contains can also seriouly degrade staging/imaging. YES- It is a possibilty that the amp is too small for the B&Ws, or the combo too small for the size of the room. Are the SPLs you are reaching satisfying? If they are: power's not the problem. Have you had good sound stage presentation in your listening room, with the rest of the system and those speakers, prior to replacing your power amp? YES- IF everything else is of quality, balanced and set up correctly: good NOS tubes should profoundly affect your reproduction.

It seems to me that in order to have a good sounding presentation, the type of tubes play a very important role than the system (amplifier) itself. Is it true? Right now, my amp is unable to produce a wide soundstage. Is it the amp unable to drive my B&W 801?

Here is a site that describes the presentation you can expect with various 6SN7 tubes. (http://home.att.net/~chimeraone/6sn7sound.html) I've personally tried all the top 6SN7GT/VT-231 variants mentioned, and have found the Sylvania 6SN7W(tall bottle) to have the most accurate bass reproduction and slam(hated the short bottle). The Tung Sol round plate(oval mica/metal supports) is the winner for sound staging width/depth and ambience retrieval. They are both tonally neutral and faithful to the signal. Next for neutrality and sound stage performance are the Ken-Rad VT-231 and Sylvania 6SN7GT(bottom getters from the 40's). There are a variety of good 12AX7 tubes that will sub for what you've got from Telefunken and Siemens. My personal favs are the ECC803S(tele) and E83CC(Siemens). Here's a site that describes the presentation of some of the variants: ( http://www.tubeworld.com/12ax7.htm ). You'll have to be careful/picky shopping for ANY NOS tubes, as the market is flooded with cons. The KT-88 is an easy tube to replace, but not with NOS. The prices are nuts nowdays. Upscale Audio sells the latest iterations of the Winged 'C' KT-88s and 6550s, from the St Petersburg plant, either of which will provide nice bottom and clean mids/highs. Their matching, testing, grading and burn-in procedures are second to none. (http://www.upscaleaudio.com/6550KT88-Types_c_85.html) Of course: good sound staging/imaging is VERY dependant on your speakers, system balance, room acoustics, etc. BUT- you are certain to hear a marked improvement regarding the realism of your presentation with the above mentioned tubes.

I suggest checking with the manufacturer on substitute tube types, but, that aside, I also recommend that you listen to your new amp for several months to let it settle in, determine its sonic signature, and exactly what about its sound that you like or dislike. The 6N8P's are equivalent to 6SN7's. In current production I like the Electro Harmonix gold pin versions, but these are readily available and reasonable priced such that you can check for yourself. In NOS versions, there are several web sites that you can google but for me, I have found that Ken Rad's deliver the best bass punch (atma-sphere m60's), RCA (or other) 5692 red base for the best midrange liquidity, and the elusive Tung-Sol round plate VT231, for tonal correctness (way too expensive, and a LOT of used up tubes being sold as new, so beware), and I am told that the Russian military metal base is highly regarded (no personal opinions here). The 12ax7B are available from several chinese manufacturers and are promoted as a deluxe version of the 12ax7 (I can't help you here because I am just not familiar with whether or not the "b" version is a true upgrade. The KT 88's are probably your most expensive tube to replace, so I would not personally change them out until you have to. In any event it MAY (check with your manufacturer) be substitable for EL 34's (better mids) or KT 90's (better bass), however your amp may require biasing the output tubes when changing them, so again, READ your insruction manual and CHECK with the manufacturer! Happy Listening and enjoy your new amp. Sincerely