I have received my Brainwavz hamburger pads for the Quad! Well they're more like a happy meal compared to your Big Mac
@Anatman
Here they are sitting with the HD600, which has similar fenestrated leather pads from Dekoni.
So first the bad news: there's no way I can make them fit the Quad without reusing the plastic part from the stock pads, because they're smaller than I thought! I should have picked the XL round pads that are much wider as Chris suggested. I might do that later because the good news is that I like what I hear!
I didn't expect such a big difference in the top end. The Quad is now a much darker headphone than with either the stock velour or the leather pads. Gone is the bright top end, the focus is now on the bass and the full bodied midrange. The difference is even more spectacular than when I switched to the Dekoni pads on the HD600, and I like both headphones much more this way.
On top of that the bass is rumbling like crazy now, there's no comparison with the velour pads that sound thin in comparison. I think the transparency is not optimal because there is an additional foam layer that comes attached with the pads, but the sound is still quite clean and sharp overall, no complaint here.
In direct comparison with the HD600 which is a bit my benchmark tool at the moment, the Quad has a very similar tonal balance with much deeper bass and a livelier midrange that has a lot more presence and never feels hollow at all. Yes I said it, the midrange is better! At least on my setup (Fiio K5 pro). I think this says a lot about how well the drivers are tuned on the Quad once you find the proper pads.
These are early impressions so take it with a pinch of salt I'm definitely keeping those pads on the Quad and probably upgrading to the XL round version shortly to have a better fit.