What is a better route, tube or SS preamp?

Everything sounds pretty good, but I want it to sound great!

In a way it will depend on the genius of the Designer (they are all genius, but there are differences ), there are good examples for one or the other design out there.
But, at the end of day, when a signal goes through the vacuum of a tube, something happens, no transistor can do. Most lifelike reproduction I heard were based on tube preamps.
Tube Design has a lot of differences, I would look for a design which is soft on tubes (some designs burn them really down), reliable, silent and pure in tone. In a way, a good reason to travel around to learn ....

If you go the tube pre-amp route, newer ARC pre-amps are fine choices for all kinds of music, including rock and metal. I would be cautious with some tube pre-amps though especially for this kind of music. I use an sp16 with Class D amplifiers. It is hard to tell what amplification technology is used. It just sounds great! I like that!

Be aware that if you go tube pre-amp, output impedance is higher and for rock/pop/electronic music in particular to sound best, clean and dynamic, you should make sure input impedance of you amp is 30K ohms or greater. Many amps designed to work well with tube pre-amps are 60K ohms input impedance or higher. My Bel Cantos are 100K ohms input impedance. The higher the better though benefits of going too high may be marginal or not significant.

If not sure about impedance matching between a tube pre and SS amp, stick with a good SS pre-amp. I would be looking at Bel Canto pre-amps if it were me.

I also replaced an old Carver pre-amp with the ARC sp 16. Huge difference! Definitely worth a try!

In this hobby hopefully you'll eventually be able to try (own or at least audition at home) many different designs which will eventually refine your personal taste.

At my age the idea and practicality of lightweight and powerful solid state has been a hopeful search from the first 60's A/B to todays class D switchers. Underneath this silly quest was the reality of the second order harmonic presentation of tube amplifiers that I grew up listening to in radios and televisions from the fifties.

I came full circle last year and purchased a pair of affordable Bob Carver VTA 180s. Cool running, easy maintenance, and more than enough top to bottom power for todays speakers. Having rolled my third set of input tubes their presentation evolves, something that can't be done with solid state.

Don't get me wrong I'm not plugging tubes I'm just enjoying them, again. I still have a pair of Hypex nCore 400 switching amps in my studio. Nothing like a massively powerful solid state amp. Keep in mind what those people are using to make your favorite hard and heavy music.

I think you should try both designs as the old line between solid-state and tubes has been blurred. Most good designs these days are relatively neutral in tonal balance but you can still find the old "tube sound" or "solid-state" sound if you want it. IMO, it is good to get tubes somewhere in your system, and if so, tubes are much better suited to voltage gain (preamp or input stage of power amp) than they are at current gain (output stage of power amps). I have had Conrad-Johnson, CAT, and Essence tube amps and they do all of the things SS amps do. However, since you have a tubed CD player output (don't know if they are voltage gain or cathode followers), a good SS design may be just fine. I think you are correct in listening to both and see what you like best.

"I know I need to demo some of both, but...”

No buts; that’s the answer.