Need some treble

Second the recommendation for a Schiit EQ -- they have three options. The Loki Mini is only $150 and offers four bands. The Lokius is $300 with six bands (and offers balanced XLR in/out as well as RCA) and the top-of-the-line unit is the Loki Max for $1,500 which is six bands but with all the stops pulled out (relay potentiometers, full inductor coils, remote control, etc.)

If you are streaming and using Roon software, Roon DSP is the ultimate tone control.  No special hardware required.

Did you verify that the tweeters in your speakers are working?

Can you adjust your seating position so your ears are at the same level and directed towards your tweeters or tweeter array? I have the same problem and even small adjustments can make an audible difference. Listening near-field will help too if you can.

I'm not streaming. Strictly records and CDs.  Tweeters are working.