Forgot to state, that to answer your root question of how to best hear “tubiness”, you want an SET. Single Ended Triode as well as being Transformer-coupled.
An OTL, such as a Dark Voice, is another choice for primarily high ohm headphones.
A hybrid having tubes & chips, while nice, are just that, a hybrid, such as an Aune T1.
A Push-Pull tube amp will give you more power, though you would want one with control over feedback, where life gets canceled out; these ones get more expensive.
The APPJ amp is a tiny SET, as is that Inspire by Dennis Had. The downside of an SET is distortion, your control over that is the component selection and design, where the cost comes in...