Okay. So I'm sitting here with these Castle Howard S2s that I've just plonked in place without spikes or anything. Pretty much as expected really. No nasty boominess - apart from one large one that makes people sound quite nasal. I'm beginning to suspect the room more than anything else. However, they are detailed, although laid back. Lacking punchiness even at reasonable volume (these have 90dB sensitivity), I decided to fiddle. I turned off the Class-A output on my amp, which turned the output up from 25W RMS to 100W RMS per channel. This did wonders to the dynamic-ness of the sound. And again the same with the source direct button. With it selected, the sound was flat and lacked stereo imagery; with it switched off (ie. passing through the bass and treble controls which are turned to neutral) the sound comes to life.
I will have to fiddle more and try the Mordaunt Short 914s again.
The Suzanne Vega bucket test is passed :)
I'm pretty happy with these and don't feel afraid that I'll grow to dislike them; they suit the room. I'm not blown away but then I don't think I can be with the rest of my setup.
My current leaning is to keep these unless I can find something better, and I do plan to keep looking.