Digital Audio Player

I have a FiiO X5 digital audio player. I hook up to my home hifi system through the Bryston SP3 preamp and then to the Mark Levinson 333. It sounds OK but my question is will a DAC necessary? If yes which DAC is suitable and if not what are your recommendations.
See here for an in depth test:
Pretty good, therefore. You might just possibly hear an improvement with an external DAC, but it would have to be a rather good one like a Benchmark DAC3.