Yes, semi synthetic 2T can mix with synthetic 2T.
Not sure what 2T is good for the SP but the common popular ones
seem to be the Castrol TTS, Esso and Mobil brands. There are a lot
of other brands like Motorex, Plutoline, Motul etc etc. I use
Yamaha's Yamalube for my TZM as it was specially formulated for
Yamaha bikes.
My opinion is that the 2T you use depends on your riding style. If
you do not rev your bike above 7000 rpm normally, then semi
synthetic 2T is good enough. I used to use Castrol TTS but since I
ride very sedately, a lot of oily residue gets trapped at my
exhaust. Semi synthetic was more suitable for me, cheaper too.
