How are most audiophiles going from streamers to DACS

Newbie question, looking to purchase a high resolution streamer.  What I don’t understand is people hooking coaxial digital or optical to their receiver.  I thought optical and coaxial didn’t have the full resolution that hdmi has for the new formats.  If you’re using a high quality streamer, even with a decent receiver, shouldn’t you use the the RCA out to take advantage of the DAC from the streamer?

Thanks! 

Typically optical is of poor quality. SP/DIF (RCA) or AES will have full resolution. Music streamers normally will not have HDMI outputs, those are for home theaters.

A streamer can have a DAC with it. Normally if you talk about a streamer it wound be assumed not to have a DAC. But there are all sorts of combined units. If the unit is a streamer and DAC, then there is likely single digital output for connection to an external DAC and dual RCA analog (and maybe dual XLR) outputs for connection to a preamp.

Make sure you are not mixing up fiber (i.e., optical) in lieu of Ethernet for purposes of bringing the digital information to the streamer vs. toslink (i.e., optical) as a means of conveying digital signal from the streamer to the DAC.
The first is in no way a compromise compared to Ethernet (although some will argue that it depends on the interface).
The second, optical toslink vs. electrical coax is discussed in this paper. BTW, Charles Hansen was founder/owner of Ayre Acoustics. If you click on his name at the bottom of the article it brings you to more discussion than you probably want.
In short, both toslink and coax can sound fine although coax is typically considered better...unless you start talking to folks who use USB.
Here is a post discussing USB vs. S/PDIF, which favors the USB interface, primarily because of the benefits of asynchronous mode USB, which slaves the source (i.e., server or computer) to the DAC.  However, according to the author, S/PDIF interfaces have  improved to the point where there is virtually no measurable or audible difference between the two, when properly implemented.  This is beneficial to those who still spin discs with a CD transport, which typically output through S/PDIF.