The thing with the Nox chip is that when it was released, the PSP rate of fire was still 15.4bps. Like older Tadao boards, the minimum achievable rate was 14bps. At 15.4bps, the Nox chip does indeed shoot three round bursts, but at 10bps, that may no longer be the case. Unfortunately, I cannot check that for you, as both my DM5 Nox chip and my Nox Shocker board are both out of date, and still only adjust down to 14bps. Being in the UK, I've not sent them in to be updated.
A newly bought Nox chip, or one that has been updated, will adjust down to 10bps, but whether that then limits you to two shot bursts, I cannot say.