Sure, I use a Sonos to a Tube DAC to a tube Pre then a tube amp. I also have a modded Red wine ipod into a tubed electrostatic headphone amp. I really wouldn't use the excuse that tubes "smooth out harsh MP3s" marketing speak. First you shouldnt be listening to MP3s on a high quality system. They sound bad over anything and you need at least some of the higher bitrate lossy files or better yet lossless such as WAV, FLAC, apple lossless. You cant bandaid flawed media. Solis State amps sound good too and my use of tubes is preference and the ability to tailor the sound. I also have a couple high end solid states that I enjoy very much. Like I said you would do yourself a favor by listening to high bitrate ad especially lossless files than throwing money at fancy docks- tube or not.
