Your wanting what all business owners want (TriMedGroup rings a bell where have I heard that b4? Dr's/chemists?) They want to go from their comfy yet limited SE 6 seater to something that's not much of a jump up operating cost wise but want a lot more from it. Yr talking about an entirely different ball game here. C206 great plane in it's class but in order to have an airframe go faster carry more or same (6/7 bums) in a twin package you will need to jump miles up the ladder. A light jet is a whole other game. Yr boss likes fast a new you say, yr C206 sale price would be lucky to buy a couple of turbine wheels etc, that's how much a jump yr boss is thinking here:-)
Still if the need is there then money will have to not be the impetus for making the right choice.
Beech C90 or any Beech for that matter would be a good choice. Reliable, fast & will carry the bums needed, & will land on the ruff stuff also. But they are not cheap! Going from a piston plane to a turbo prop means $$$$$$.
C310? yeah not too bad but awful things pax wise for access.
Islander? Flying noisy slow box............pass
Seneca?..........pass
PA 31...........another big jump up from the C206 but even though still very popular few around these days that are sweet.
Out of the twin piston jobs to do what you ask here the AC50 Shrike might be worth a look at. Tough, good load carrier (7 bums) reliable donks with props way above the ground for ruff stuff & fast enough to cover most of what you want. Trouble is they like all the other twins in that class are old, find a good one & yr set
Basically it's either piston twin or Turbine twin (SE if yr game !) Pick one they are both very different beasts, then stick to it:-) The little 'slowtation' looks pretty but is a toy amongst small jets but once you have flown a small jet you won't want to go back to 'boats'
Wmk2