This is a rather old thread but since it’s been resurrected, I read through it and want to add my 2 cents to it.
I don’t have the Plantronics BT300 but I have the BT600, designed to work with my Plantronics Voyager Focus Bluetooth headset. But I think it works on the same principle.
I thought that the BT600 (or the BT300 for that matter) is simply a USB dongle that interfaces between your PC and the headset. If your PC has Bluetooth, then you can probably pair it directly with the headset and don’t need the USB dongle. But if your PC doesn’t have Bluetooth, you can use the dongle to be the middle man to connect between your PC and your headset. The USB dongle also help make things more seamless when using soft phone apps on the PC like Skype for Business (or previously known as Lync).
But I don’t necessarily believe that the communication between the BT600 (or BT300) to the headset is via Bluetooth because there’s no need for discovery and pairing between these 2 devices. They just seem to know each other’s presence and communicate to each other automatically. I actually use 3 separate BT600 dongles on 3 different laptops I use, with a single Focus headset, and as long as the laptops are not on simultaneously, the headset just works with whichever USB dongle that’s currently on connected to the active laptop.
So while the headset is a Bluetooth device, the USB dongle doesn’t appear to be a Bluetooth device. It’s not the same as a Bluetooth USB dongle that adds Bluetooth support to your PC. It’s designed only specifically to communicate with the Plantronics headset it’s designed to pair with.
That’s probably why nobody on this thread has been able to pair the BT300 with their Bluetooth enabled HA streamer. If you want to pair your streamer with a PC that doesn’t have Bluetooth support, maybe buy an adapter like this one https://www.amazon.com/Plugable-Bluetooth-Adapter-Raspberry-Compatible/dp/B009ZIILLI/ref=sr_1_3?ie=UTF8&qid=1490574362&sr=8-3&keywords=bluetooth+adapter+to+pc from Amazon and try to pair it with your streamer. But note that this is just an example, I don’t own this adapter nor do I know if it’ll work for your streamer.