Do you guys exchange dirty talk outside of the bedroom? If not, your suggestions of what to say may be pushing him beyond his current comfort zone. This would be counter-productive.
It may be easier, less pressure for him to open up outside of the bedroom first. You know, not at the heat of the moment. Try getting him to engage with a fun, flirty and playful tone. Maybe a naughty text or suggestive phone call. Don't rush it, take your time. Ask him questions. Get him to respond. You are trying to get him to engage. Once you can overcome this barrier, it will be easier for him to speak up at game time. You can then gradually escalate to naughty, dirty, filthy or vulgar talk, whatever you both want, but only after he gets up to speed and gets on the same page.
It took my wife and I, years before we both felt 100% comfortable saying anything and everything to each other. We love it. It has greatly enhanced our relationship, both in and out of the bedroom. It is definitely worth the effort.