I’d not start with DAP tube amps, as they are a pricey relative to conventional amps and/or power limited versus a regular amp. To minimize your exploratory costs, go with a simple design such as the Bottlehead Crack or others like it. It has only two tubes, and no need for finding and buying matched pairs. (Matched pairs often cost more than two unmatched tubes of the same model.)
You might also look into a tube buffer stage, as they (1) are modestly priced, and (2) can be inserted between the DAC and any solid state amp. They can be used for speaker or headphone amps, and become functionally similar to a tube hybrid amp.
I bought a Nutube buffer evaluation board and built a sandwich case. No tube rolling possible with the NuTube, but it has four settings, and each channel can be tweaked independently. It’s educational if nothing more.