Power cord with warm treble + very solid bass ?

there you go MrTennis balanced frequency response with no exaggerated treble or no leanness.

Dealer/Manufacturer disclaimer

My interpretation of warm treble is rolled-off treble. There are many, many power cables that do just that. But those really limit the capabilities of a great system. Why spend tens of thousands of dollars just to sweep a perceived flaw under the rug?

Really, you want your system to have very extended treble that is free from grain and accentuation. You also want a balanced and linear cable. I would recommend you try NVS copper and silver series, in addition to Tripoint Thais.

I'm also a bit surprised you perceive the cable to your tubed preamp as the source of your discomfort. Are you sure it isnt your CD player or amplifier PCs? Another tip, while I don't know your system or how it is set-up, is to potentially remove a couple degrees of toe-in. For some speakers, the tweeter can hit your ears before the midrange and cause some accentuation. Rotating the speaker will balance detail and focus vs. warmth and smoothness. Also, it will change sound stage width and depth from narrow vs. wide. You may need to find the sweet spot after any component change.

get a preamp with tone controls or find an eq. better yet, get different speakers!

A Sablon Audio Robusto is exactly what you're looking for.

I can recommend VH Audio AirSine and LessLoss. The AirSine has been in my system longer than any of them and LessLoss has been a good one.