Congratulations on your purchase.
Typically systems sound better with a preamp… most of the time and significantly. But occasionally they will sound better without. Typically without a preamp they will sound very detailed, but flat and without soul. However, given the high quality of the DAC vs the rest of your equipment you will have to try it.
I would put your new DAC in your system and get it broken in. In this time you will get to know what it sounds like. Then switch to direct. If it is not immediately obvious which is better.. then when you switch back to using the preamp it should be.