How to proceed?

@stuartk 

OK, just greenlighting by an amateur (me).

I was going to recommend fine tuning with a Lokius, which I own, but I see no go.

It is puzzling in that you have dome tweeters.

Could your tweeters have ferrofluid?  If so has it possibly dried up causing what you are hearing?

If me, I would first purchase a new coax cable to rule that out before big changes.   Even a cheapie something off monoprice or amazon just to rule out a cable problem.   Actually, you probably could just use a standard RCA interconnect as a cable test. 

That's all I got.

@mahgister

I only say that the dac may not be the problem in itself but the synergy on some frequencies response never mind if it is very good on some other aspects between it and the rest of gear

If this is true, then would logic suggest swapping out only one component at the time (DAC, Amp or Transport) might not be sufficient -- that I might have to try multiple combinations of components? I ask this because you are better at logic ! ;o)

@jetter 

RE: ferro-fluid, I’ll e-mail Silverline.

Really-- a standard RCA IC ? OK...

@stuartk 

Really-- a standard RCA IC ? OK...

I thought I mentioned, not for long term listening, just to make sure your current coax cable (assumption you are using coax) hasn't been damaged in some unforeseen way i.e. doggy gave it a good bite.

@jetter

Coax isn’t damaged and is not within reach of dog. ;o)

Sent message to Silverline. 

Here we must ask for experienced people not for logic 😊...And i am not an audio engineer for sure... Myself i will try an other dac to begin with, any other one to see if the problem stay with me ,  ...Synergy is always a three partners affair mainly, dac- amp- speakers, where one is the main culprit ...

But more experienced people here will advise you perhaps better ...

@mahgister

I only say that the dac may not be the problem in itself but the synergy on some frequencies response never mind if it is very good on some other aspects between it and the rest of gear

If this is true, then would logic suggest swapping out only one component at the time (DAC, Amp or Transport) might not be sufficient -- that I might have to try multiple combinations of components? I ask this because you are better at logic ! ;o)