I just got the 890 and also have a PS3, with a similar setup that you have: TV, A/V receiver, etc.
1. Out of the box, the 880/890 will NOT be able to turn the PS3 on or off. The reason is the same that you cited, PS3 uses bluetooth from the controller to turn it on and off. The 880/890 is IR, thus it cannot send the correct command to the PS3.
2. However, the Harmony will do everything else that you stated, and that's how my remote works now. I have a "Play PS3" activity on the remote, which, when pressed, turns on the TV and A/V receiver, sets all the proper inputs on the TV and receiver, and away I go. One button press and the system is ready minus having the PS3 on.
One positive development recently is that Nyko has released an IR-based remote for the PS3 which includes an IR receiver that you plug into a USB port on the PS3. This would enable us to use that Nyko remote to "teach" the Harmony remote all of the PS3 commands, and with an IR receiver then the Harmony could control the PS3 for movie watching or XMB navigation.
The only unknown with the Nyko remote is if it replicates the PS button functionality (used to turn the unit on/off mostly). I would hope that it does, but I haven't seen this confirmed anywhere.