Please post what you find with regard to speakers suitable to match power delivery of your amp. Is there any wattage specs for your amp?
If you haven't already, you may want to read the 6 Moons review of this amp (link included below). I also included paragraph from this review that may be helpful. I don't consider the statements relative to speaker use as outlined in this article, to be conclusive, but rather, observations.
In fact, the HA-02 with a pair of superior headphones could be slightly preferable to the A-08S with speakers. That's because the Yamamoto is way overbuilt for its intended headphone-drivin' task and, as a high-gain pentode design, get's away with a single stage. As a quasi linestage device, it is presented by a load that doesn't have its triodes strain. Instead and like flowers, they stand erect in a wind-still niche, blossoms open, fragrance undiluted by gusty conditions. In that sense, it's an idealized greenhouse scenario. Conversely, the speaker variable, how it interfaces with the amp plus unpredictable room interactions could be anything but ideal. I've owned my audio-technica wood-cup 'phones for years. Truth be told, I didn't know they were this good. No headphone amp before has quite maxed out their potential to this degree. That's a lovely bonus for me. Never mind that the two together have a very similar finish. How would the Yammy work on 32-ohm Grados and 300-ohm Sennheisers? I don't know. I've long since sold my HD-650s. For my tastes, the W1000s ran circles around 'em and were far more comfortable to wear. The Sennheisers could be somewhat of an impedance mismatch on this amp but I'd have to hear them to know for sure.
http://www.6moons.com/audioreviews/yamamoto4/ha02.html
If you haven't already, you may want to read the 6 Moons review of this amp (link included below). I also included paragraph from this review that may be helpful. I don't consider the statements relative to speaker use as outlined in this article, to be conclusive, but rather, observations.
In fact, the HA-02 with a pair of superior headphones could be slightly preferable to the A-08S with speakers. That's because the Yamamoto is way overbuilt for its intended headphone-drivin' task and, as a high-gain pentode design, get's away with a single stage. As a quasi linestage device, it is presented by a load that doesn't have its triodes strain. Instead and like flowers, they stand erect in a wind-still niche, blossoms open, fragrance undiluted by gusty conditions. In that sense, it's an idealized greenhouse scenario. Conversely, the speaker variable, how it interfaces with the amp plus unpredictable room interactions could be anything but ideal. I've owned my audio-technica wood-cup 'phones for years. Truth be told, I didn't know they were this good. No headphone amp before has quite maxed out their potential to this degree. That's a lovely bonus for me. Never mind that the two together have a very similar finish. How would the Yammy work on 32-ohm Grados and 300-ohm Sennheisers? I don't know. I've long since sold my HD-650s. For my tastes, the W1000s ran circles around 'em and were far more comfortable to wear. The Sennheisers could be somewhat of an impedance mismatch on this amp but I'd have to hear them to know for sure.
http://www.6moons.com/audioreviews/yamamoto4/ha02.html