It seems to be a Tandy 1000 RSX which supports Windows 3.1

Original photo is from here, which has Windows 3.1 running: http://www.oldskool.org/guides/tvdog/RLRLX.html

It's a 386SX, which absolutely will run Windows 3.1 but if you're going to be real picky, it definitely won't be as snappy as in the video ;)

Question is, would you be able to put a Soundblaster 16 inside it?

Tandy 3-voice can play midi without an add on card.

Right but I know Yamaha OPL sound when I hear it.

The Tandy 1000 RSX has several ISA expansion slots. Putting a Sound Blaster in it is no problem.

The irony is, Windows was developed on Tandy hardware. Because it had more CPU and graphics oomph than any IBM offering up through the AT, Microsoft developed Windows 1.0 on the Tandy 2000 and shipped it with drivers for the PC. A driver disk for the 2000 itself was available.