I like the SMSL SP400 more than the Topping A90 and even the HeadAmp GS-X mk2. (Owned 'em all.) It has better precision and detail, and can drive any non-exotic headphone, including the Hifiman Susvara. It has a similar design to the Benchmark HPA4, but with more power.

I am the original owner. The warranty lasts until November 2023 and will transfer to you.

It comes with the original packaging and accessories. (Remote control, manual, power cable, etc.)

Price includes the PayPal fee and insured FedEx Home Delivery shipping. (USA only.)

For more info:
https://www.smsl-audio.com/portal/product/detail/id/725.html
https://soundnews.net/amplifiers/headphone-amps/smsl-sp400-review-a-flawed-masterpiece/
https://www.audiosciencereview.com/forum/index.php?threads/smsl-sp400-review-headphone-amp.19346/

I have an all-in-one unit now, so I am parting with some of my gear. If you buy multiple items, I can give you a discount. Here are some other items I have available. Send me a PM and let me know which ones interest you.

power cable: Virtual Dynamics Master
https://www.head-fi.org/classifieds/virtual-dynamics-master-power-cable-1-meter.17655/
music server: Musician MDP-2
rare single driver loudspeakers: Omega TS3
triple driver loudspeakers: Polk Monitor 40 Series II
power amp: Behringer A500
headphone cable: Venus OCC Silver/Copper & OCC SPC Litz Wire Braided Cable (with 2.5mm headphone connectors and 1/4" termination)
headphones: beyerdynamic DT 990 Edition 250 Ohm (rare blue version; needs repairs)
equipment rack: SCS Portable Studio Rack 6RU