I think you can use two controllers with no profile (guest).

No it's not. I'm pretty sure it's some bluetooth thing. You can only connect 6 controllers if you have a wireless headset connected.

The wireless headset gets a controller number, even if it's not a controller. If you play alone, it gets number 2, if you play with a friend, it gets number 3. You'll never notice, but with 6 people, it gets number 7.

Now, if you play with 2 people and 2 headsets, the headsets get number 3 and 4. 

Bluetooth itself does not have a limit for devices.

no... it was a bluetooth limitation, from what i can remember, the total devices  paired was 8, being the actual PS3 one of them. i have 2 bluetooth head sets and lots of controllers, so i will test this out today after work.
also move controllers just have one led and they work as controller 7, 6 , 5 etc... the 1-4 leds where just a visual representation with not such importance.
with bluetooth todays newer and better specification, that is no longer a issue as we can see here.

I didn't think you could even connect two headsets to the PS3 at once. Never tried. But I know for a fact that it is not the LED's that are causing the max of 7. If the LED's were the problem, the max would be 9.

Just checked, you people are right. A master Bluetooth device supports only 7 devices. My bad. Though I am certein I heard somewhere Bluetooth doesn't have a limit. Ah, well, nevermind.

There are 14 channels, you need to have spacing between channels to prevent signal bleed over, so each device occupies two channels.  This means it can support 7 devices.  A similiar thing happens on the Xbox 360 with Wi-Fi, except in this case the channels are coupled for bandwidth as well as providing a bleed-over barrier.

In the Xbox One, multiple channels are combined -- up to 4 based on my calculations  -- three for bandwidth and one to prevent bleedover.  The difference is that unlike the Xbox 360, the Xbox One's channels aren't tied to a device.  So, you can have 8 controllers with no headsets.  But if you start adding headsets, then the number of controllers drops.  Four headsets, four controllers.  

And only a 10 games will support local multiplayer.

Just saying, =p

You may not have a limit on the number of devices that can be connected, but you do have a limit on the number of devices you can connect at once.

The limitation is with frequencies, frequencies that translate into channels, channels that translate into actual devices.  For each device you have a channel or group of channels that the device transmits/receives on, and one to provide a separation from bleed over. 

Bluethooth 3.0 have the same limitation?