I did not change the tubes in my DAC.
But last time I used a Furutech ADL USB cable to connect my desktop to the USB input of the DAC and did find it a tad too bright. I then connected my desktop to a Singxer SU1 DDC and used it to connect to the coaxial input of the DAC, the sound was decidedly more pleasing and less bright.
I bought an Oyaide Neo Class S USB cable, tested it both direct USB and with the Singxer. The Oyaide sounded really good with direct USB, smooth, just a touch brighter than with DDC/Coaxial but with better soundstage and imaging. Ditched the Singxer and used only USB cable now. So, the quality of the USB cable did matter in my case.