You can find a lot of information about the Qutest and other Chord DACs in the context of systems based on Naim amplifiers in https://community.naimaudio.com/t/dave-came-round/3367/689.
In my view the old Naim DAC is a great value for money if you can use it bare. If you think that you need a 555PS to make it work in your system, I would perhaps look elsewhere. The other way round: I would not mind investing in a 555PS with the old nDAC if I knew that Naim will come up with an nDAC successor that can also be powered with the 555PS. But it seems unlikely that Naim will come out with an nDAC successor.