How much would I lose going to a Bluesound Node 2i

That is an impossible question to ask. We cannot tell you that what you hear with the Node 2i will be better or worse than what you have. Those are your ears, your brain and psychology. But the Node 2i is considered a budget component, therefore you can buy it, listen to it, compare it to your Aries and Metrum and report back to all of us. You can tell us what your ears told you!
I have the Node 2 and having experimented by connecting it to my Benchmark DAC and the Bifrost Uber DAC. Both routes sound stellar, but when playing MQA albums on the Node 2 with it’t internal DAC, it sounds the best to my ears. Others here do not hear any kind of improved sound with MQA. So it has to be your ears to decide for you.

The OP poses an interesting question.  I won’t be able to fully answer it but perhaps he may benefit from my experience.
  I have the Node2 and the Vault2.  The weak link in both is the DAC and for both I use external DACs.  None of my DACs do MQA.  When Bluesound added MQA I tried a few recordings via a 10 day Tidal membership.  I limited myself to recordings that were already in my collection.  My DACs are the Bryston DAC 3 and Mytek Manhatten I.  For MQA I used the DAC in the Vault2.
   The MQA albums that listened to were compared both to CDs played on an Oppo transport with SPDIF out into my DACs and CDs that had been burned into the Vault2.  I preferred listening non MQA
with either the Oppo or the Vault2 as a transport.
  When I compared ripped CDs from the Vault2 via the Internal DAC compared with MQA from Tidal via the Vault2 the results were inconsistent.  Sometimes it was a marginal improvement, but not always, and in some cases the plain vanilla from the Vault2 was better.  In every case I preferred my non MQA DACs by a wide margin.
  The OP seems more taken with MQA than I was.  My advice would be to stop worrying about the links in the chain if the end result sounds good.  Perhaps try the Node 2i (which is supposed to have a better DAC than my current Bluesound components) but hang on to the Aries (is it upgradeable via firmware updates) in case they embrace MQA.

+1 Mahler.
I think MQA is just another gimmick to make us buy an unnecessary product. A well recorded high rez recording holds up against MQA.
As others have said the Node DAC is good, but at least you can bypass it to a DAC of you own choice.
I use an Ayre Codex and have nothing bad to say about this combination.
B 

I have the Node2i and when I bought a Benchmark DAC3B  to use with my old Onkyo CDP I also connected the Node2i  to compare and to me it depended on the recording some I thought were  a little better through the Node2i  some the Benchmark   which does a partial unfold of MQA to 24/96 but it was really hard to tell. I also thought the same recording in CD sounded better on either so Someone with better equipment  and ears than me might hear a big difference  I never did. To the OP all I can say is you will need try for yourself.