There might be another way to look at it that could be really useful in this scenario. Rather than saying that you don't want it to happen, instead, ask yourse

There might be another way to look at it that could be really useful in this scenario. Rather than saying that you don't want it to happen, instead, ask yourself what changes would make it so that you would be okay with the change? For example, if the CUXO was willing to sign over half of his stake (10%) to you, would you be okay with him taking the CTO title? You could argue that giving him the CTO title will give him a future leg-up in career and earnings that you should be compensated as well. If the CUXO is not okay with that, than you have a good argument for keeping things the same.