I use a CB6 as the centre channel speaker with my IB1s, as I could not accommodate another IB1 because of its size. I have mine set to 'small' in the SP1 menu because I don't want it to detract from the bass of the IB1s. I find it is a better match sonically than the TB1+ I used previously. In my setup it is plenty loud enough (using 4BSST for the IB1s and 3 chan 9BSST for centre and surrounds), and it performs its main function of locking the dialogue to the display very well. In particular I don't feel that an expansive soundstage for the centre speaker is necessary, since this is already well provided by the IB1s. However, in the form of the OB1, from which the CB6 was developed as the matching centre speaker, it certainly has a large expansive soundstage.
In short I'd recommend it in this role, notwithstanding the fact that an IB1 would be better.
