I have no experience with these, but I do know the D50s DAC wit the A50s amp and, budget willing, the P50 linear power supply for that stack, is very well thought of.
It didn’t come up in my general search, but I think ShenZhenAudio usually has the stack with and without the linear PSU with a discount available.
Why not the Topping DX3 Pro+? Offers a lot in a combined package. But what about your iFi Zen DAC makes you want to upgrade, I thought the Zen DAC was quite good.
It doesn’t have nearly enough power for the headphones I want to purchase. It pushes out 330mW at 32 Ohms balanced, but for example the SP400 has 6W at 32 Ohms, almost 20 times the power. But I also worry the Burr Brown chip of the iFi Zen DAC isn’t ideal and the output voltage isn’t high enough for the amps I mentioned
Only Topping or SMSL DAC I’ve ever actually liked was the DO200 and the only amps from either of them I’ve liked were the SH-9 with an A30Pro in a distant second place. A DO200+SH-9 stack might not be awful.
What do you need single digit Watts for? Blowing your eardrums into a low earth orbit?
Unless your headphone is extremely inefficient (≤ 90db/mW), you do not need anywhere close to one Watt, never mind more than that.
And I get doing the kids trading card routine of “my thing has higher number” is fun and all, having headroom so your amp does not run out of breath when that drum solo kicks in is also good, just stop it with the absurd “MOAR POWA!”-meme.