Since you already have two Echo Studios, just put them in a group along with the Echo Sub and you can play music that will come out of all three speakers.
As for using 2.1 speakers, you can only do that via a wired connection (using the AUX outlet from the Echo) to the 2.1 speakers. If you want to go wireless, it's either several Echo devices in a group or one and only one Bluetooth speaker.
An alternative I just thought of just now is to use a Bluetooth receiver, which then connects to the 2.1 speakers via a wired connection.