There no chance i can demo these two together in the UK!
I have already had extended listening sessions with the Lehmann and was mightely impressed.
Yes, choose 0dB, 10dB, 18dB, or 20dB. I usually use 10.
I have PS1000 and the M-Stage drives it very well. The only downside might be if you are looking to dull the Grado highs just a tad, which a tube amp will probably do for you but the Matrix/Lehmann will not. I personally do not have issue with the Grado highs so it works just fine for me.
As someone said already, the Matrix/Lehmann is very transparent, and will not change the sound for you, so be aware of that.
The GS1000i sounded terrible with the BCL considering that the BCL sells for $1000 here in the US. The Grado GS1000i is very neutral and does not have the traditional grado highs. It sounded so boring with the BCL that I eventually sold the combo. im using a Sim Moon Equinox cd player as the source. I would presume that the PS1000i has a similar sound. Get a vey powerful amp that is happy driving the low impedence Grado's and make sure that the amp has a signature tht you enjoy listening too. The Grados do not distort so you can play them pretty loud as well. Also the Grado Gs1000i has pretty weak bass extension compared to the HD800's so you would need an amp that can really extend low to balance the GS1000i out. Once again Im presuming that the PS1000i has a similar signature. Also the GS1000i had a decent level of resolution, hence make sure that your equipment is not one notish or the GRADO will sound very dull and boring.
I heard the PS1000 with a BCL clone. The sound is acceptable but to make it very good you need a couple of modifications inside of the amp. I re-built the output buffer adding some JFET transistors, removed the LP filter from the input circuit, replaced the op-amp with two singles, using a trick to bump up the op-amp input stage bias currents, replaced the rectifier diodes for 15ns soft recovery and then I can say this amp is very (not ultimately) transparent. The slight drawbacks are about 10 ohm output impedance (for big Grado's - the lower the better) and some offset voltage which does no harm to the headphones but could be smaller i.e. when pairing the transistors and output resistors. I was too lazy to pair them as I did it for the experiment and to find the right mods I do for my friends buying the BCL or its clones. I usually use another amp which has no offset and vitually zero output impedance and is better.
The PS1000 surely deserve a hi-end amp, this one is just very good but only when pimped up in several fields.
As someone above said, the BCL is void of sound signature - that it is fairly neutral. PS1000s should work with the BCL/M-Stage provided you have a warm (but not bloated) DAC or source. I owned an M-Stage which I performed significant mods on (though not to the extent of majkel) and it worked well with my Sony X portable (very warm and fuzzy).
But if you have a neutral source, stay away from BCL/M-Stage (even though M-Stage is supposedly slightly warmer than BCL) for PS1000s. The big Grados are very picky about what they are mated to. I've had a love-hate relationship with them.