The 300-1 is not a 2 channel amp, it has 2 sets of speaker terminals for convenience, it is a monoblock rated to do 150x1 @4 ohms & 300x1@2 ohms. The punch 300-2 is a 2 channel amp rated for 75x2 @4 & 150x2@2, 300x1 bridged@4.
biggest difference between any mono and 2 channel amp, is the impendance load they are rated at... when running a 2 channel bridged, the 2 channels are still seeing independant loads (in a sense) ... thats why most 2 channels are rated at 4 ohms bridged, while their mono counterparts are rated at 1 or 2 ohm mono