Tube Rolling - No Change in Sound

Ken-Rad VT231 has been known to deliver excellent bass and sweet mids. Sounds like you didn't get any of that! Well, at least, you will probably be able to easily sell them.

Sure sources (and preamps) affect sonics, but with them, it's basically "what you buy is what you hear" -- they are what they are. The reason the amp+speaker=primary system sonics is because:
A. Once a signal is created (by a source) the amp processes the signal (multiplies it by a huge factor) more radically than any other device (even including equalizers!) A line preamp (not a phono preamp) is really a signal switcher + a buffer stage; it selects a signal (source) and then optimizes it for driving an amplifier; but it doesn't really alter the signal that much; not compared to an amp!
B. The speaker (and the speaker/amp interface, AKA how much the amp likes the speaker it's driving ;-) is the other major factor that determines a system's sound character. Don't tell me about the room treatments, and the cables, and the temperature and the altitude ;-) they're all important. Nevertheless, you can do anything you want upstream, but horns, stats, cones, domes, ribbons, buttons and bows! each have their own unmistakable sonic character -- and you can't make one sound like any of the others (not by any legal means ;-)
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I don't know if I agree, in my system amps have made the least difference, speakers the biggest difference by far - then source followed very closely by preamp and lastly amp.

I do agree without question the amp/speaker interface has to be optimal or close to it or you can throw everything out the window.

I am an inveterate tube roller and some circuits will not respond to tube changes.
I tried to cool off a highly modded ARC SP6B pre amp. It already had the reputatation of "legendary gain gone wild." You can't simply swap lower mu tubes to get a more viable midrange and travel on the volume pot. It takes 12AX7s x 6 and only Only 2 are in supposedly real meaningful gain positions.
Try as I might for example with top of the heap 5751s -some real low mu 12AU7s, those almost passed enough current to burn up my spoeaker's voice coils, the amp seemed to care less.
The only result was a change in tone with very, little if any perceptable change in gain
I know it is purely anectdotal and can't hold a candle to the concise asnalysis above. The technical answer is the cathode follower bleeds freely into a leak grid intended to dissipate and not redirect the amplified electron velocity. A very loose lowest impedance pull if you will on the the gain. The other tubes are phase splitters/inverters which have no gain function except as input tubes. That is a matter of keeping the input signal at a predertimined voltage. This is required for the rest of the pre to "hear" the signal.
Now I am going to roll some 6SN7s yes Rodmann even though I have many inluding 4 pairs of TS RPs and Ws tall and short metal bas or black. I also have a few Kentucky Radio , National Union including the gray and several black but today I think I will try TS WGTs - NIB pristine NOS. I am not sure what they will sound like a priori.

Wax, cotton swap