I thought that might be the case - I've been thinking about building one to go with my recently acquired Grado SR225's and the question of which opamp to use has been occupying my 'daydream' time for a little while now.
Actually, RS are showing these as "Extended range items" so they're not available from stock and may be subject to extra shipping/handling charges.
Farnell don't stock them in the UK but you canorder from their US sister company Newark via Farnell for an extra 12.95 s&h on a 3 day delivery.
Digikey will also ship to the UK but I haven't checked if they stock the AD843
I just came up with a very simple design myself starting with the straightforward chip and two resistors. Adding a bias current to take it into class A then running into a buffer due to the low impedance of the grado phones.
I'll draw a schematic once it's built as there will definitely be some changes.
Once I'm happy I'll be trying to get it all done with surface mounts to try and keep the signal path short.
The designs I've seen on the web (cmoy variants) look fairly straightforward.
I've been thinking about building a PIMETA - the design isvery similar towhat you describe - i.e classA bias with opamps driving buffered outputs. You'veprobably seen it already but the details are here