the Sentinel is a business class unit I am not sure what the hardware differences are if any between the two I do know that the EX4 is a prosumer device based off the Sentinel.
Personally I feel the EX4 is well underpowered in terms of CPU and RAM. it’s painfully slow network speeds are well documented here in the fourms. It’s current removal of NFS support has been a bitter pill to swallow for advanced network users.
Regarding streaming TWONKY DLNA is a pain and lacks features yet the underwhelming CPU and RAM and slow response to people looking for the SDK to develop for it is apathetic.
My personal recommendation is to shy away from this product, I own one and wish had spent the slightly more money on a higher performing, richer feature set and more robust community around something like Qnap or especially a Synology. I think you look around in the user fourms here you’ll find that expressed frequently.
Try Small Net Builder .com. They have a very comrehensive list of objective and performance reviews in thier NAS Ranker section. You will find both the DX4000 and the EX4 including afore mentioned hardware specs.