Hello Jacques,

I did some research once. translate with google :-) Sorry...

I'm not sure if I'm going to use the UE32M5570 with a Sennheiser tv headset (3.5mm jack)?
-> Yes, it is possible to input the optical signal, and the coaxial output via a 3.5 mm jack. Please note that an external power supply is required. USB cables and 230V connectors are included FiiO.

Can I also connect a Hifi with a CINCH-CINCH cable?
-> ? no, coax to optical or optical to coax. It is a converter

Is a TOSLINK optical audio cable supplied? -> No, it must be ordered separately.
The Value Toslink cable (1m, Entry, Black) is good

Thank you, perfect and clear answers