The Burstbucker Pro #2 in the bridge is more subdued than it is in my (solid) Les Paul, perhaps termed a bit more "woody".
The P90 - heaven. Then again I'm fan of the P90 - and this one is rather hot as they go - close to 9k (Gibson runs 'em about 8.1-8.3k mostly).
The middle control cuts mids as you turn it down, keep crankin and you get a sort of subdued bottom with a sparkly top tone - the bottoms there, but its like you've cut back but kept the top the same, so all the sparkle is retained. A nice, and useful tone.
Treble control, works as you'd expect - also nice taper on the Warmoth/CTS pots. Good rotational changes in all three controls.
In series the pickups are PHAT. You get a slight volume increase, and a huge huge low end, no loss of highs but the bottom mondo.
Semi-phased - hardly any loss of volume (less than half as much difference as going normal to series on the pickups. just perceptable loss), You get that phased mids tone, retain the high end, and retain the low end since its "semi" phased. This is NOT like having one pickup stronger than the other and only partially phase cancelling. It is a true "semi-phased" operation whereby the signal from the neck pickup is passed through a capacitor. When that happens you get a phase rotation of... its early my brain isn't working... 60 degrees I think. You can say its 1/3 out of phase or 2/3 or whatever - its semi phased.
And... as a bonus... through magic of the electrons... if you play in any mode on the rotary switch, and crank the mids and treble down you get this strong upper mid tone.... that sounds exactly like playing through a stationary MuTron phaser (ie non rotating). The classic example of that is at the end of "Killer Queen" - right at the end where there is a chord played in rapid succession over and over, as the phaser does this sort of arpeggio downward. Well "that chord tone" is what you get. Not totally useful, but different, and hey... it dont take batteries to get it.
I'd really like to thank Bill Lawrence for the idea he had, that got me thinking on this circuit, which is a very versatile one. He had no involvement, other than to tell the story of how he wanted the L6s to sound like, and how Gibson cut him back on dollars. I tried to recreate what Bill might have first envisioned, according to his descriptions.