Is the Mytek Brooklyn Bridge or Lumin D2 good buys in 2021?

I would not separate the dac from the streamer because of several reasons.  First, internet music nowadays are streamed in much higher bit rate with a lot of information and it's up to the receiving end i.e the dac to be able to process that.  Having all in one streaming DAC would eliminate the need for possible noise in the transmission via the cable.  Yes, the signal is digital but both ends will have to do extra processing of the music stream rather than doing 1x.  Second, the best cable is the shortest cable so doing this, you achieve avoiding signal integrity issues between your dac and streamer.  Processing streaming data from network to music format is done once.  Network is one of the most realizable transmission of signal because it has data and security error handling built in the protocol.  Third, you might save money on having to buy two units along with interconnects.   The PS DSD DAC is probably one of the best DAC for the money to be able to accommodate all these while still provides the flexibility to be used as a pre-amp and standalone DAC. I was looking at the X1 streamer and I came across 1 person who had them both for comparison and yes, the X1 is tiny bit better but for 2x the price, new or used,  and most importantly, X1 can't be used as a standalone DAC.  X1 has the latest and the best processors (2) SABRE DACs that can process 32bit data stream so you're future proof but I haven't seen any streaming service that provides that 32bits content.  TIDAL is maxed out at 24bit for their MASTER subscription.

cleed, you're right to a certain extend.  If receiver can be build to handle the high current and maximum peak power from separate amps then it's actually better.  The advantage of advance technology occurs everywhere but in this particular example, where signals are passed between difference processors, the less travel the better for the signal integrity.