Interesting way to introduce tubes into a system and very affordable. A tube equalizer actually makes sense in that people use tubes like an equalizer to flavor the sound to personal preference. Would love to hear it.
I had a tube DAC once and enjoyed rolling tubes with it. Each tube had a unique sound. Best to try several and see which floats your boat. In the end I decided no tubes sounded best and went with a different DAC model, same design but no tube buffer.
Also had an Audio Research tube pre-amp (sp16) for many years. It sounded wonderful but again in the end I dumped tubes all together and that's where I am now for several years.
That's just me. Everyone is different. It's like soup. No one recipe is everybody's favorite.

