@amirm Thank you for the review, can you please add measurements for XLR out? Sinad, multitone, crosstalk and so on. With remote control, this device is interesting for those who are looking for preamp with headphone output. It's good alternative to Pre90.
I own Topping A90 for 6 months already and SP400 for one month. I'm more in to loudspeakers than headphones, so my headphone comparison is limited to AKG K701 headphones.
As headphone amp I prefer A90, it's slightly more calm and smooth tone balance at higher frequencies is more pleasant for long time sessions. With SMSL SU-9 DAC it's dream match, to me better sounding than A90+D90.
The SP400 is always slightly more transparent and does uncover everything. With SMLS SU-9 it's sometimes too much and the higher frequencies can be aggressive. Topping D90 is better match to my ears, the SP400 extracts every little detail from it, yet for long session it is not hurtful.
Anyway my current favorite headphone rig is A90 + SU-9.
For loudspeakers I need more time, but my current feeling is, that SP400 will be better, but i need to work on DAC. SU-9 is sometimes still little aggressive and D90 has it's own problems with female vocals and details rendering (I attribute this to output LM6172 buffers, I regret, that with D90 Topping omitted option to easily replace output opamps). My amps are Hypex NC500 monoblocks without input buffers and loudspeakers are Thiels CS2.4.