Stuart, you may find on this forum more that one or 2 people have equipment like this as well, and maybe a full spectrum analyiser too, I would go as far as to agree agree with on the measurements front, I have GB's of data to surport how/what your discribing, however as I said before something shouldn't make any difference, and there is no Physical or sicentific reason either, but yet they do

Lets take the pen, now you state you tried 2 discs and it made no difference, I would also agree  However I have plenty of discs which do benefit.

A lot of cd manufacturers do treat the inside of their players lids, draw and transport compartments with green paint, even the wadias (later ones) uses green platter and spinners.

Now, just surposing we bias up the photodiode emitter, with say a outside source, emitting into the laser head area, that is configurable & switchable, carrying it's own indepent powered source, and then hook up a scope & full analyiser, select a suitable constant test tone, measure the effect first on the scope, the a FS run, then place a indentical treated disc and preform the same preocedure, I will place a small wager that you'll see no measureable difference, on the S/A, or any thats visiable on the scope trace, however I/can and others in lab (who are bigger sceptics then either Tones or Ranson), not all the time for sure.

Now change the bias of the light wave length of the laser, then see what happens, then preform the pen test again  most interesting.

At the end of the day, they'll will be strong pro's + Negitives for both sides, with various evidence brought forth from either camps, you have your own ears Flawed or not, it's your reference, I' haven't got golden ears or particularly special hearing, however I can tell a difference from sound that is different from a know reference, which is used for an origin.

Still as Merlin would some thing to get your teeth into  Wm

BTW we don't sell the pen