Which DACs are known to be sweet/rich/relaxed?

That is correct.  The Oladra or K50 have two computers in one box (with separate power supplies) along with an elite clock.  

My understanding is the Pink Faun Ultra is very, very good but their top performer is a "double ultra" which is $47K which is one Ultra as Server, one Ultra as Renderer.  With Pink Faun, it is all about the clocking and they have superior clocking to just about everyone.  I am considering adding Pink Faun as a brand but haven't personally demo'd it yet.  

I work with the North America importer for Aries Cerat and Pink Faun and I know they work well together. 

If the Lampi Pacific has a bridge available that is great.  I do not know how it compares to the others mentioned above.  I will say this.  I feel that Antipodes K50 player and clock outperforms the Weiss Player in the DAC 501/502.  It may be that that K50 (or Pink Faun, etc..) might outperform the network bridge in the Pacific.  

I still say the Trinnov Amethyst would be your best investment if you’re determined to spend $25K. You can create settings to your particular tastes for different types of music. It would do much more than wires or tube DACs or overblown servers.

The Tambaqui is a very neutral DAC and you are actually hearing the recording artifacts. Higher model Lampizator is not going to sugar coat a bad recordings, which most of the rock albums are. Those DACs will be more detailed and are supposed to bring more than life like images. You might be able to change the flavor by changing tubes.

I would suggest two things:

1. Try a Weiss 502 or 501. They have filters, like a vinyl emulation, which can tune the sound and the DAC is slightly on the warmer side which will favor rock music.

2. Change the Nucleus into something better. The Nucleus is not upto the snuff with the rest of your gear. If you are into Roon, try a Innous or a Lumin u1.

Try an Aesthetix Pandora Eclipse DAC if you can.

@robert1976 I am in a similar boat. My system is also very enjoyable but, tends to get bright and harsh with certain (rock) recordings. I don't listen at higher volumes so that is not an issue. I too am not unhappy, just curious if I can chop off that bright top end with certain recordings.

I was thinking about taking a slightly different approach. Purchase a less expensive Dac that would only be used for poor recordings. Something that tones down a hot top end. Dacs I am considering are a used PS Audio direct stream or Lampizator Baltic 3. I will also look at used Audio Note Dacs.

So what I am looking at is an Aurender 200 feeding a Berkeley Alpha USB then AES to a Berkeley Reference 3 and SPIDF to the new Dac. Both DACs will be connected to my preamp.

I did compare the Berkeley to the MSB Premier and preferred the Berkeley. One caveat is the new Dac must have balanced output.

Are there any other DACs I should be considering that will only be used for about 10% of the music I will be listening to?