Can i connect 3 bass cabinets to a Blacksmith, the same as with the RH450 or RH750. For example a RS410 + RS210 + RS212 connected to one blacksmith output of 4 ohms?
No, the Blacksmith is not like the RH450 and RH750, which have a minimum load of 2.66 Ohm, whereas the Blacksmith has 2 Ohm.
But the rule is simple : if the load is below 4 Ohm, you must set the switch to 2 Ohm. Then you can connect 3 cabs to only one output if it is more easy for you or you can use both - they are in parallel.