When CD was released, it was all done in the one box. Then someone had the bright idea to separate the functionality into two boxes, transport and DAC with an interface (SPDIF ). This was the first level of added complexity, As you add more interfaces the complexity increases. Having an external clock also adds complexity.
Simplicity is when you have all the essential aspects close together with optimised interfaces. Examples would be:
- the source as in CD optical drive close to the DAC connected by a short I2S bus;
- the clock should be as close to the DAC as possible to minimise jitter;
- not having multiple inputs and outputs with selection switching and extra processing/digital devices;
- digital devices are essentially noisy on the power supply, so the more processing you have the more noise;
Naim were very smart when they designed their first CD player, the CDS, in that they made it 2 boxes with all the essentials optimised in one and the power supply in the other. They also used the best of the Philips transports and selected 1541.
A rebuilt CDS with better parts (audio grade capacitors, UF rectifiers, improved regulators, no digital filtering/oversampling) and a clever analog filter would be something special.
The modern trend for digital is to have as much functionality/options/inputs as possible with everything externalised and connected with uber cables. Those that I have heard always sound wrong to me.