DACs/Amps:
Unsurprisingly, Pro 82 prefers clear, detailed amps.
Amps only:
O2 (1.0x/3.3x) sounds best (in high gain) , it has the largest soundstage among all amps when used with Pro 82
Oppo HA-2 as an amp is second best, sounds almost the same as O2, except smaller soundstage.
Little Dot MkIII and
Nobsound NS-02E take away too much of Pro 82's clarity (although some may find the coloration pleasurable)
Oppo HA-2SE as an amp sounds veiled (DAC is as great as HA-2)
FIIO E12/E12A sounds very good too, just introduces a little bit of warmth.
FIIO E6 sounds good too, even though it's far from being Hi-Fi -
especially with ELE EL-D01 DAC
Little Bear P10 Excellent hybrid amp,
has the same great synergy with ELE EL-D01 DAC as FIIO E6
Amp/DACs:
Oppo HA-2 as a DAC/AMP sounds very good to me.
Oppo HA-2SE has a more transparent DAC than HA-2, but the amp is a bit veiled.
NFB-11.32 sounds too colored from the headphone out, much better through the variable out - but still not as clear as HA-2.
GeekOut V2 sounds similar to NFB-11.32's variable out.
SMSL Idea sounds a bit too dry as a DAC/Amp, but when used as a DAC with O2 amp (1.0x/3.3x, in high gain) , it becomes very musical -
best combination for Pro 82 so far.
SABAJ DA3 sounds better than Idea as a standalone DAC/Amp,
but lacks the synergy with O2
SMSL IQ sounds better than Idea or DA3 as a standalone DAC/Amp,
but lacks the synergy with O2
xDuoo XQ-23 sounds excellent with Pro 82,
but is ruined by it's firmware/usability issues
D1-Mini is a good option for bassheads, turns Pro 82 into a bass cannon,
upgrade over most laptop outputs
Lusya "SA9023A + ES9018K2M" provides high quality warm sound at ~20$,
as long as you keep the volume under 75%
Hilidac Audirect Beam 2 is overpriced for its sound quality, but
offers MQA rendering and a balanced output
Sabaj DA2 sounds
exactly like SMSL Idea and
retains its synergy
Lusya ES9038Q2M sounds very good standalone,
but lacks synergy with Pro 82 and under-performs other DACs based on the same chip.
FIIO BTR3K sounds extremely well standalone,
borderline synergy with Pro 82.
Hidizs S9 sounds quite colored,
better when paired with O2.
LG V30 sounds very good in high gain mode
HTC 10 sounds very similar to V30 in low gain mode - not too good.
Ahmadfaizadnan's impressions of Pro 82 with iDSD Micro BL
Ahmadfaizadnan's impressions of Pro 82 with iDSD Nano BL
Bankbail's impressions of SMSL Idea and O2
Miguelbazil's impressions of SMSL Idea and O2
About synergy
Of course, this is all highly subjective, YMMV