Rupert Neve's RNHP & beyerdynamic Amiron (not great)

Wonderful reviews all around but I am disappointed. Headphones: beyerdynamic Amiron Home. DACs: either Fiio M11 or RME ADI-2 DAC FS. Cans are 250 Ohms.  For Fiio I bought a balanced cable from beyer: definitely much better result than 3.5mm, especially to drive 250 Ohms. I was hoping to further improve the sonic experience with this well regarded amp. But as it is, the results are not better or even the same -- they are obviously worse than even Fiio driving beyer by itself (with that cable).  
I first connected Fiio 3.5mm to RHHP's RCA with Audioquest Big Sur. Most definitely not a 'wow'. Then I tried balanced XLR cables from the RME DAC to RNHP's balanced inputs (adjusting reference level). A bit better, but definitely worse than RME ADI-2 DAC just by itself (it sports a headphone amp). In fact, the headphones sound just amazing driven just by this DAC, so connecting this DAC to RNHP doesn't make any sense unless somehow RNHP improved on the DAC amp (and it most definitely doesn't). 
So far my "improvement" only makes things worse, which is very unexpected given the rave reviews. Either I am doing something wrong, or both the Fiio, and especially the RME, are that good already and hard to beat...

What do people think?
Neve made some highly regarded mixer consoles over the last few decades, but that does not mean the circuit couldn't be better- nothing is perfect in this world, which also means that something else can be better, and that price or reputation might not have anything to do with it, as you've experienced.

If I were you though, I would allow the amp and the cables plenty of time (at least 50 hours) to break-in and warm up, as you might find that in that time they have changed.
Yes, I will do that. Also, I just ordered very short, very high quality 3.5mm connector to use between Fiio M11 and the RNHP. You can understand why I thought that this amp, given all reviews and RN's fame -- much bigger and heavier than the whole Fiio player, dedicated, amp -- would beat whatever's inside the Fiio, especially for larger cans at 250 Ohms.

I mostly listen to loudspeakers in my "music room" -- this setup was for the "office." I now think I could just move the RME DAC between the two rooms. Perfect sound at no additional dollar cost -- at the cost of inconvenience.

Another thought: the RME is $1,100, so "only" $600 more expensive than RNHP, but it is DAC/AMP and truly great in both dimensions. One can therefore consider buying the second RME DAC instead of the RNHP.  I found a review today ( comparing the RME to Mytek Bridge. The reviewer prefers the Mytek but only just a little bit... But Mytek costs almost 3 times as much as the RME. I would never spend 3 grand for this functionality, given how great the RME is.

In any case, I'll give the RNHP a couple of days of a chance before my return window closes.