AV2 connected to Pioneer BR player via coax digital and to Apple Airport Express via Toslink.

Very different gains between the two sources.

When watching, for example, a DVD DD soundtrack, AV2 volume is typically at 75 - 80 whereas a volume level of 45 - 50 will produce the same level of loudness when the Airport is being used as the source.

Rest of system includes 282 and V175 for centre and surrounds, with 200 for front pair.

Is this normal?

BR

From memory with a unit sporting AVC0107/F658, 0db is 82 on volume. (Although be carefull of running this level through your speakers!)

Try using a source that has both coax and toslink outputs and then compare the inputs that way. This way its a reliable test (assuming the source device has the same level on both types of output...).