B&W 803D vs 803Di

The 803 Diamond is overall the better loudspeaker as you would hope (and expect) for a newer version. But it is not a dramatic improvement - move akin to a BMW mid-life automobile face-lift where the engine has been upgraded and and a few cosmetic exterior changes applied. The only cosmetic update I really appreciate is the magnetically attached grille - makes it easy to remove for serious listening.

The 803 Diamond is marginally more detailed in midrange and treble, and has a tighter and more articulate bass. The 803D midrange and treble are better matched in sensitivity whereas the 803 Diamond treble balance sounds slightly tilted up.

Overall I think the 803D is better balanced tonally for relaxed listening whereas the 803 Diamond is a touch more upfront and rewards more focused listening sessions.

Is it worth the extra money? Depends on the cost differential and how far you will go with your front-end electronics. The 803 Diamond will definitely reward better front-end electronics - e.g. the difference between my two SACD players is that more obvious, although both are still enjoyable to listen to.

Thanks, Mark_nz. Given your answer, how would you adjust it if these were to be geared more for theater experience rather than music? Say, 90% movies, 10% music.

Assuming other considerations are equal (age, condition, finish preference etc), then for movies I think the savings will be better rewarded by upgrading the AV and projector.
The 803D/HTM2D is more than good enough for movies. However if you really very picky about voice quality, the 803/HTM2 Diamond may be sway your choice - recommend you compare the HTM2D and HTM2 Diamond.
Also for background music the 803D is very good; most of the improvements for the 803 Diamond will only be appreciated when listening in the sweet spot.

If you can go and have a listen. The newer range is vastly superior in my opinion.

I compared the B&W 802D against the 802 Diamond at a Hi-end dealer. Same room, same electronics, same music and loudness levels. From my experience these two systems sounded almost identical. Scary close IMO. Even the salesperson thought they sounded very much alike. While I didn't make a comparison of the 803D and 803 Diamond, I would have assumed a similar outcome.