The new SC5000 Decks offers analog and digital outputs with RCA connectors. Of Course the X1800 has both inputs to connect the media players.
My question is: Are there hardware limitations of d/a conversion of the player or the mixer? Can they convert D/A in the same quality or do they offer different hardware and results for this? With wich connection will i get the best sound? Or sould i use another D/A hardware after the X1800 Mixer like the RME ADI?
You’re overthinking this. Use digital connection to the mixer whenever possible and worry about your source music quality and gain staging more. The only mixer that is worth by-passing it’s DA conversion is DJM800.
You’re going to get the X1800’s sound no matter what if you’re using it, so you’re not going to bypass that by adding the SC5000’s ADC stage’s sound to the mix. Stay digital.
No harm in trying your RME as an outboard DAC for the X1800. The new Denons have nice DAC chips and the X1800 has a nice associated analog output stage, but I have no idea how your RME sounds and variety is the spice of life.
Only digital DJ mixer where the DAC had a bigger influence on its default sound than its DSP was the Numark PPD01, also from InMusic, and with an outboard DAC it’s amazing how good it sounds for being one of the first 24bit dj mixers.