Jarraa- To answer your question on the Spirit III (or II), The front two 12AU7's are the input tubes, and the back two 12AU7's are the driver tubes. By using the direct input of your amp, you are NOT bypassing either of the two sets of 12AU7's, you are only bypassing the attenuator and the input selector section of the amp. I am currently using the direct inputs on my Spirit II, and using a Lightspeed attenuator running to my CD player. I miss being able to use the remote volume control of the amp, but gain a bit more detail and clarity with the Lightspeed.
It is most noticeable at the very low listening levels I am forced to use late at night when the kids are sleeping.
It is most noticeable at the very low listening levels I am forced to use late at night when the kids are sleeping.

