Single-plug TRS stereo connections are almost never used in professional applications. These connections are unbalanced, and hence notoriously prone to picking up hum and other interference. No good. Do use a proper pair of balanced mono connections if you want decent results.
The single relevant exception is headphone connectors. Because these are low-impedance lines to a device with no other connections, they aren't subject to the usual interference problems.
So basically the only kind of device that will do the thing you're asking about is headphone mixers/distributors. The JamHub is such a device; it's pretty neat for monitoring (I use it often in band rehearsals). But there's no way around it: you need to be prepared for a lot of nasty hum as soon as you connect more than two other devices.
For that matter: I don't see the point why you want single-plug stereo. If you want to drive two active speakers, you need two mono cables anyway – from the mixer to either speaker. The only sensible solution is to have an ordinary-professional-style mixer with all mono plugs. Use an R/L breakout cable (⅛" TRS → 2×¼" TS, or possibly 2×RCA) from the tablet to the mixer. This is an unbalanced connection, but should be ok as long as the tablet isn't grounded through a charger. Then two mono XLR cables (or TRS balanced mono) from the mixer to each speaker.
