Hook up two US-20x20 via toslink

[Lania]

First time posting. I only own an audio interface by Tascam: the US-20x20.
I love it. Sounds good, works perfectly.
I have two questions:
1) Is it possible to hook up two units? I need to add analog inputs. I already own an optical converter device. I can add 8x analog synthesizers. Unfortunately, this device has a low quality. It generates a hiss noise. I would use the second US-20X20 as this device connecting it only with the toslink. Will this work?
2) Can IN1 and IN2 only accept Mic and/or guitar? I don't sing and I only use my bass from time to time. I mostly use synthesizers (lot's of them) so those two are two input less for me to use...

Thanks in advance for your input!

Regards,

Lania