Multiple Bluetooth speakers simultaneously
You cannot use the same Bluetooth device profile with more than one deivce at the same time.  You won't be able to do what you want to do.

For a listing of all the different profiles, see this Wikipedia entry.

But I can have multiple Bluetooth devices paired to my iPhone.  I have a keyobard, a headset and speakers.

Each uses a different profile.  Your keyboard is considered an HID (Human Inteface Device) while your headset uses the HSP profile and your audio (speakers) likely uses the A2DP profile.

These profiles are 1-1.  Meaning one profile to one device at a time.

If you want stereo get a stereo receiver that supports Bluetooth.