I don't personally think there is a veil with the Senns (and I own Grados for comparison) so that is something you will have to determine on your own.
On the amp front, I like the Quads being driven by fast amps. NAD classic amps (C320BEE, C350 & C370, all of which I have heard) make terrible, boring parings with the L-series speakers. Rotel and Cyrus amps will work great with the Quad. I have also heard them paired with the Roksan Kandy and the higher-up Caspian amps. These aggressive-sounding amps, while not really a virtue I like for an amp, worked so superbly with the Quad I see the reason why WHF mag likes them so much.
Cheers!
Edit:
For comparison sake, I own the 12L and pair it with a Cyrus 8 amp. This combo IMHO sounds more euphonic/musical/more fluid (you get the idea) than anything my own headphone rig can conjure up.
[size=xx-small]Sometimes I wonder why I am wasting money on headphones when I still prefer my original stereo setup[/size]