I have just brought some Mordaunt Short speakers for my setup to replace my old speakers. When I looked at the sub its got L and R phono connecters for the input, but my yam amp 620 only has one sub phono output. The speakers are the Mordaunt Short and the sub is the 308 Whats the best way forward here. Would it be ok to buy some sort of doubler to make the phono doubled output??