Ultralinear and Triode. What's the difference

Yes, an old thread, however  great one! I bought a used Line Magnetic 211ai which is EL34 output based and runs in triode and ultrlinear. I just received it and played in in UL yesterday. Going triode today.  I bought it for exploration. Wanted to hear the difference between modes of operation and also to see how a lower watt tube amp can drive my Tannoy Sterlings.  I have heard the Line Magnetic 845 integrated amp which was lovely. Should, after discovery, I choose to I will likely sell the LM211 for a more upscale amplifier. In the past I didn't have the resources to explore my passion in audio. Now that my wife and I am retired and have put 3 kids though college, one each BA, MS and PhD, we can direct funds toward our hobbies. 

Audio-fanman,  I am not the one to answer your question as a reason for reviving this thread, but thanks for doing so. Please forgive me for my intrusion.

Regarding the LM211, I believe I like the triode mode better. The 15wpc seems to drive my Sterlings to as loud a level as I want in my 12.5 x 14.5' room. I imagine the LM211 is operating in parallel triode mode to deliver the 15wpc. Still have much to learn and experience about tube amplification. 

I have a Aric Audio Special all tube 6sn7 based preamp which drives my BEL 1001 MK5 (13 years old) which is tough to beat at my price point. When the time comes I am thinking of replacing it with a Pass XA25 amplifier. Also wish to own an all tube integrated, yet to be determined. Giving my power requirements I am not sure I can go SET. 

Dennis Had has designed a lot of amps and I've owned a couple of them. The Inspire Firebottle HO (High Output) I currently use (few years now) is designed for Single Ended Class A Pentode use. He's described the design in detail here and there so look around if interested in that, but suffice to say his amps are astonishingly well made point to point wired sonic masterpieces.

From the original posts, sans the heat, I gather:

SETs = 1 triode/channel = low number of high quality watts.

Parallel SET = 2 triodes/channel = more power = some concession on quality?

Pentode and tetrode (P/T) tubes can be wired as triodes, many feel sound better this way.

This not to say P/T tubes wired in triode sound better than a pure triode. However maybe supply more power?

Would love clarification/correction in my gatherings. 

My Muzishare X7 uses KT 88 tubes,  I have a issue with a pop in one spesker when I turn off in ultra linear, but if I turn off in triode it does not pop.

I guess what I'm getting at do those different modes use different parts of the tube?

Could they it be a tube issue?

Amp is brand new