Why Do Some Recordings Sound Great and Others Dead?

Recordings vary widely in SQ, as I'm sure you know.  Some seem to agree with your system and room while others don't, and some will never sound good.  They're just bad recordings.

You say the acoustics in your room are poor.  Can you do anything to improve the room?  That's probably what you're going to have to do.

I listen to RP a lot and the quality is pretty consistent, especially on the Mellow Mix station. Question, how are you controlling volume in your chain? Node, SMSL, Beolabs?

I believe the only way I can control the volume is through the SMSL DAC.  I use the SMSL remote.  I bypass the NODE DAC and use a USB cable to send the signal to the SMSL.  Under ‘Audio Settings’ and ‘Select Output’, once I have connected the NODE to the SMSL it reads ‘Default’ ‘SMSL USB AUDIO.’  The Beolabs have no volume control.  For my subs, they have their own volume settings for their volume in the system.

Too much compression (dynamic range), overuse of limiters, microphones not set up properly, bad mixing engineer, bad recording engineer.

Or it could be the (most likely) Wolfson DAC chip in your iPod. Many people agree that Wolfson DAC chips are on the sweeter side of neutral, rather than clinical sounding.

[Verse 1]
Sunrise, sunrise
Looks like mornin' in your eyes
But the clock's held 9:15 for hours
Sunrise, sunrise
Couldn't tempt us if it tried
'Cause the afternoon's already come and gone

[Chorus 1]
And I said
Hoo-ooh-ooh-ooh
Hoo-ooh-ooh-ooh
Hoo-ooh-ooh-ooh
To you... 

great song

A couple suggestions:

1) I assume you have 'Audio Level Fixed' set on the Node? Not sure that is settable if you bypass the DAC, but make sure it is set to pass through.

2) Try listening to RP's FLAC lossless stream instead of MQA. MQA adds a lot of complexity, maybe some songs are not being expanded correctly.

3) Looking at the M400 manual, it is pretty lean on explanations, but I see reference to various filters, phase and brightness settings. Not sure these are all relevant, but maybe some adjustment could make a difference.