SMSL SA300 - just no, one guy joked that it's a good headphone amplifier with its power. Actually I'm a low-level listener in a 14m^2 room so I don't mind low power, but 58dB SINAD? Come on.
https://quantasylum.com/blogs/news/first-look-infineon-merus-ma12070
Feel free to check specs of Yamaha receivers but it takes a lot of desk space.
Never ever check Youtube reviews of audio gear without measurements. These guys live from creating hype. The latest fad on ASR is linking rave Youtube reviews in Amir's measurement threads of headless panther award winners.
PA3 is TDA7498E, so 62.5dB SINAD @1W according to the datasheet, not too good. Quite a lot of power but a very high fail rate according to reviews. TDA7498E amps don't have a good reputation in longevity.
1. What
@Xulonn recommends, would be one of the good bets. Aiyima has a few TPA 325x amps. The TPA3255 without Bluetooth has a bad pop sound, even confirmed by the manufacturer. You also don't want to buy the newer TPA3255 with Bluetooth because it usually means more noise. TPA3251 has slightly better results in datasheets than 3255 - apart from power that still should be more than enough. Very cheap, $40 when on sale + about $20 for AC/DC Adapter (32V 5A), no reported pop sound. Datasheets say it shouldn't go lower than 72dB SINAD but I'm skeptical with this cheap implementation.
2. What
@bunkbail recommends, Allo VOLT+ D (DOUBLE). Supposed to measure almost the same as Volt+, so 70dB SINAD (manufacturer data). High-quality components, better than average frequency response linearity. Expected longevity. Still, quite far from an average headphone amp performance in terms of sound transparency.
3. My personal gamble, I'm very hyped about Allo's TPA3255. Release planned for September this year, info from 2 different sources. Some suckers believe it's going to be China-cheap because it's TPA-based. It won't be. In Poland, the Allo VOLT+ D (DOUBLE) is already at $135. The engineer's target is so big and competition-crushing that I don't know... Maybe I should hope it doesn't measure THIS good and I can get it for $200-250. I don't believe it's going to appear in September too. There could be some good Black Friday deal