Where to put the better cable.

At the beginning of the series. CD to preamp (if you only listen to CD (no LP)
The reason is 'garbagein garbage out' IF you put the good wire pre to amp and the modest wire CD to pre, then the modest wire starts out lessening the signal straight away, NEGATING any goodness of the better cable later on in the chain...compared to the other way around.
Putting th good cable first at CD to pre, the quality of the sound is best it can be through the pre, and then it may be lessened a bit by the modest cable.
The real thing IS to try them and see... but the logical way is: better at source.

Try them both ways and stay with which one sounds better to you. All gear reacts differently to different cables. Also keep in mind that the signal has to pass through both cables either way.

If you are using more than a CD, then putting it between the preamp and power amp will improve all the gear plugged into the preamp; not just the CD.

My most "expensive ($$$)" cable is between the CD and preamp, HOWEVER , the cable between the preamp and power amp is the best cable for that position, even though it cost less than half what the other cost. It has better "PRAT" in the pre/power position than any other cable I've tried regardless of price or assumed quality. It simply works period...

The same goes for my FM tuner. It has the best cable for it I've tried, not the most expensive.

The "better" cable should be the one that sounds better. Forget about price or quality of materials, etc..

I agree try both ways

Obviously, (though I would go cdp to pre/ always the source) no clear cut answer here. Let the ole tympanics decide for you. They'll never steer you wrong...peace, warren

It doesn't matter a whole lot. Remember, your system is only as good as its weakest link.