Well, if what you mean by platform is the motherboard, then yes, they all use motherboards, all are computers. But implementation is the key, some use pretty much stock off the shelf motherboards, some use custom built motherboard, others modify off the shelf motherboards. In order to determine which board any particular streamer uses, one has to open up and take look. You may also be able to determine board used from interior photos some reviews provide.
The motherboard provides the basis for which processor can be used, some boards can handle high level processing, others only low level. Noise vs. speed is battle here.
Rendering is the another important aspect, some use rendering right off motherboard, others modify with add on boards with better clocks and power supplies.
Power supplies to motherboards also important, some use stock switching power supplies, others have varying quality linear power supplies.
Sonore is one of few streamers using optical, whether it preferable to another streamer debatable.
I agree with OP, many manufacturers don't want you to see what's inside. I've seen some streamers priced up to $10k with not much proprietary stuff going on. I'd suggest one get a good look inside these streamers prior to purchase, learn about power supplies, rendering. Parts used important as well, quality of processor, ssd, RAM has impact on sound quality.
I recently made choice to go with custom build streamer, over $3k in parts alone, this minus external lps cost. I've looked inside many of these off the shelf streamers, very few have near $3k in parts. On the other hand, I do see some pretty nice proprietary work going on in the better ones