tube choice for Audible Illusions L1


I have a Audible Illusions L1, and it has humming noise on the left channel. I suspect it is the tube. Also, I would like to smooth the sound a bit more. The recommended and current tube I have is 6h23neb. However, I have someone previously recommends Svetlana 6n1p. I would like to try it out, but it says on the AI FAQ that "6NIP tubes should not be substituted as they require additional filament current and their use will compromise performance."
What does compromise performance means? Does it mean the tube life will decrease? But it won't do any damage on the unit, am I correct?

Also, from the tube store, I can't specify the brand. Is it important to order a specific brand?

Besides the 6h23neb and 6n1p, is there other suggestion that will help smooth out the sound, or make it less harsh?

Thanks.
gte357s
I hear intermittent hissing sound.
10-16-10: Gte357s

That could be a dirty tube socket contact/s. With the preamp turned off try unplugging the tube from the socket and plugging it back in a few times to clean the socket contacts.
I tried plug and unplug several times, and it is still there. And it is not intermittent anymore, it is a continuous hissing sound. I also switch the left and right tube, and the hissing sound move with the tube. By this, I can confirm one of the tube failed. The other is still ok. So, usually, a tube won't fail this fast, is this covered under any warranty?
Gte357s,

Sounds like the tube is bad. It can happen with a new tube.... Call Upscale Audio, 909-931-9686. Explain to them the hiss moved from one channel to the other as the bad tube was moved.

You may have to pay a shipping charge. Can't say for sure.
I contacted Upscale audio and they agree to send me a replacement tube. Excellent service, way to go, Upscale.
The Amperex "Orange Globe" are an excellent cost-quality compromise and are likely to last a long time. I have had mine for three years.