Channels 7-8 and 9-10 can function either as stereo or mono channels, depending on what type of input you plug in.

If you plug in a single XLR microphone, that channel will function as a mono channel.

If you plug in a single 1/4" signal, it will function as a mono channel.

If you plug in two 1/4" signals into the same channel, it will function as a stereo channel.

So, depending on what inputs you plug in, it can be an 8 channel, 9 channel, or 10 channel mixer.