How much do I need to spend to get a preamp that sounds better than no preamp?

Buy the New Schiit preamp at $699 using 6sn7  tubes, 
justreplace them with the Golden Lions ,and you have the =
to preamps up to 3 timesthe cost, even a solid state option if you choose to  but a Pangea sig, MK-2 power cord. Fantastic for under$900 maxed out .also upgrade the fuse if you choose to.

Your CD player is holding you back for sure ,the oppo is very good but , look into the new Lampizator. Amber3 vacuum tube dac l
enjoy the music comes just came out with a Rave li bought the demo model  ,it came with a 2 week audition ,after a 24 hr warm up I sold my very good ps audio $6k dac lithe Amber 3 is  $2750
and has a 5 year transferrable warranty ,and bu upgrading the rectifier tube ,and 12au7 tube ,and fuse makes it even better still
read the review ,