The SP-331 MK is based on the Class AB amplifier, but it's now a Class A/AB amp.  Its output stage operates in Class A mode for signals under 10 Watts, from there it kicks up to AB for a total output of 150 Watts at 8 Ohms.  Vincent says that this helps reveal subtle detail in music that's otherwise hard to produce.  

The SA-31 MK preamp is also newly configured for Class A operation.  Vincent has added a pair of 6N16 vacuum tubes to the new output stage.  The new model also ups the inputs from four to six and includes a wireless remote control. Both the SA-31 MK ($2,199) and SP-331 MK ($1,399) are available now in silver and black finishes.