Silver Pegasus
There are likely to be a few subs in the search area that we don't know about, but this press article does show that such Chinese assets could logistically easily be on site. It would explain the apparent success of surface hydrophones and iphone ear buds!
Hidden Dragon on the high seas: China's deployment of a nuclear-powered attack submarine in the Indian Ocean sign als the beginning of its strategic encirclement of India : DEFENCE - India Today