The original Hi-Fi Wi-Fi speaker company, Sonos, seems to be your fit. They have three product lines that are fully inter-operable with each other; in order of increasing quality (and obviously price): the Play 1, 3 and 5 at $200, $300 and $500 respectively.
Despite the $50 budget breach per speaker, I include the Play 5 because you'll need at least one (or the CONNECT or the CONNECT AMP) for full source computer (Apple) audio (i.e. sources from non-Sonos compatible streaming apps). The Play 5 is also the only one with an AUX, the biggest speaker and as I mentioned the speakers are fully inter-operable, so you can mix and match.
As long as you have at least one Play 5/CONNECT/CONNECT AMP connected to an AirPort Express, all models exceed your critical requirements:
The Wireless speakers I am looking for should be able to source
computer audio, and let me select where to play it at any time (yes for Apple devices via AirPlay):
- Play one of the speakers, or...
- Both speakers at the same time (2 speakers be can linked for great stereo output)
- additional speakers can all play at the same time
- all speakers can be divided and grouped individually into zones playing different music. Note: if using AirPlay, group functions are still available, however AirPlay is treated by Sonas a single source-so same music only in that group
Additionally, I would like them to:
Support AirPlay streaming from iOS devices
And satisfy almost all optional features:
- Support direct streaming from services like Spotify (with Spotify premium-yes), Soundcloud (not sure-but if it plays through AirPlay then yes)
- Allow Aux Line-In or equivalent (Play 5 only)
- Manufacturer also provides "bridge" unit that can connect ordinary line-in speakers to the Wi-Fi system
Now in contrast to previous Sonos speakers, the latest ones connect directly to your Wi-Fi and don't require the old $50 bridge. Assuming a total budget of $900 for any 2 speakers and that you have an AirPort Express (additional $100 if you don't), to stay within it you could get (in order of preference):
- (1 x Play 5) + (1 x Play 3) = $800
- (1 x Connect) + (1 x Play 3) + (1 x Play 1) = $850
I'd go with option 1 myself because it's more than enough my for average (European) place. All the Plays sound amazing, but obviously the Play 5 really fills the room, so put plug that in your bigger/more frequented room with the AirPort Express next to it. If you don't have an AirPort Express you can get one and still be in your $900 budget.
If you want to fill a large house, stretch the budget and get 2 Play 5s. Or buy 1 Play 5, test it and decide on another or a Play 3. The main lady will try, but she'll never keep you down.