"These are my two devices."
Translation:Das sind meine zwei Geräte.
In the same way that das can stand for something of any gender, before it's introduced in a sentence, so can dies:
das/dies ist mein Auto
das/dies ist mein Hund
das/dies ist meine Katze
When you start adding declension to these words, you can do it for two reasons:
With a noun:
das/dieses Auto ist schnell
der/dieser Hund ist schnell
die/diese Katze ist schnell
Instead of a noun:
mein Auto ist dieses
mein Hund ist dieser
meine Katze ist diese
The difference between the first and last examples is that in the last set diese(s/r) means "this one" instead of just "this".
So if you wrote Diese sind meine zwei Geräte it would mean "These ones are my two devices", which is grammatically different enough not to be the best translation.
I agree that both can mean the same thing, but there is a slight difference:
"These are my two devices" can refer to the only two devices in the room, or could be just two from a selection of many devices. Nothing suggests there are more than two devices available, but the conversation is about just those two devices.
"These ones are my two devices" would generally mean that just two from a selection of many devices are mine. You are referring to two devices in particular, which implies there are more than just two devices that are being considered.