I was shocked when Bill brought over his 2A preamp. I lived in ignorant bliss till he inserted the preamp between my CDP & hybrid integrated. As far as I know the CDP has good output current & the integrated's input impedance is moderate & not too low. The 2A seemed to improve the sound from top to bottom w/ absolutely no downside that I could detect. It was not expected that two extra sets of jacks, a gain stage, & another interconnect would improve the sound, & yet it did!
Now I'm considering getting a 2A preamp & maybe a straight power amp to replace the integrated. It seems dumb to go through an unnecessary preamp stage & level control.