Sound like it's expecting a stereo input then? So more like a soundbar than center channel (which would be mono)?
From the manual :
Centre, left, right and surround
Since the digital audio signal is in stereo format, the DSP5000C needs to
be told if it is a centre, or on the left or right. We refer to the DSP5000C
which is on the left when viewed from the listening position as the left
speaker.
If you have more than one Meridian Digital Speaker, the master can be
any of the positions. The choices master/slave and position can be made
independently – since selecting which is to be master affects the way the
cables run in your installation. As supplied, the DSP5000C is set up as a
centre master, but you can alter this if necessary using a Type setting
(see page 31) or in Config (see page 32).
DSP5000Cs can be used as surround speakers. In this case they are set
to be surround left or right
Obviously, you will need the Meridian remote too