Well, slap with a paddle till I call me daisy!...that HeadFi thread brings a smile to my face, I would've thought there was more mods out there but in carbon too, astounding - the revolution is coming!!!
Anyhow, the link above looks to increase the actual chamber on the positive stroke of the driver. Any increase is beneficial, there's a limited return in that equation but still the principle is a sound one (no pun intended). One has to ask why the manufacturer didn't do this?..here's the limited return part, the headphone as a package has a cost, performance and aesthetics profile. I'd assume the headband and their link to the driver housing can't cope well with the increased hang-angle in terms of mechanical performance and aesthetics. As mods though, they'd be fun to trial!...shame they didn't incorporate the extension with replacing either the forward or reward parts of the chamber, with carbon wall thickness being an advantage even more volume could have been attained.
So, our G'Bola mods... We do a lot of work for both IndyCar and F1 air boxes. This brings us into contact with people as analy-retentive as myself but not in something hedonistic like listening to music but in ensuring air, water, oil and fuel flows seemlessly thru both the atmosphere and when contained my mineral (Alloy). A great deal of work goes into the inward flow of air into the cylinder of such engines and the relative benefits of material and shape of inlet are of paramount importance.
Air turbulence is a killer to such exercises and as an engine does not require constant flow but cycled or pulsed flow minimising the effectiveness, or in this case destructiveness, of turbulence is the goal.
Certain parabola profiles are proved to be better at achieving the goal relative to flow capacity and port length - we have tested many relative to the Grado envelope and we've designed one that we feel exhibits the best results.
Our G'Bola design is a press-on fit (we feel ease of use is key especially when performing back-back test with one set of cans - the easier you can do this the more often you'll be reassured the product works) and allows the Grado "i" range to come alive in 3 significant regions; presence of low frequencies, dispersion of high frequencies (the nemesis of the Grado range relative to the Alessandro offerings) and spaitiality. The increase flow of air in and out with the decrease in turbulence between pulses allows the above detail, that already exists but is masked in general use, to be clearly audible.
Like all things audio the extent to which this effect works is relative to the quality of recorded media, the more detail in the more detail received.
Of course, it's not all good news - you end up looking like Princess Leya from Star wars! But I always tell people if you're listening in public with Grado headphones (or any open back units) you've missed the point...

Danny