How to match preamp and power amp?
To determin "if" you need passive preamp (no gain) or an active preamp (with gain). There was a test that was a very good indicator, and that was the "Revels’ Bolero Test". This cd starts off extremely quite for quite a while and builds slowly.
You do a direct connection between source and poweramp (no preamp) making sure if it has it the source’s volume is up full.
Switch everything on and press play to start "Revel’s Bolero" just for safety have your finger ready on the source’s stop button if it gets too loud as it get’s into it.
If it get too loud or is way over your normal listening level, then a 10kohm passive preamp will do you fine, like the $49 Schiit Sys. If your poweramp has 33kohm or higher input impedance.https://www.schiit.com/products/sys
If the sound is not loud enough even over 10mins into "Revels Bolero" then you need a preamp with gain, a Schiit Saga or Freya are great buys also, these can also be passive as well as active