FOR ME, 
with the new rme after almost 7 years with the other interface,
diff was night and day

RishiS
I get more I/O at a much lesser price from focusrite  than RME or MOTU but the preamps would be the same as the 2i2.So I want to make sure I get better sounding preamps and DAC for the money if not more IO.As Bat indicated if I can hear better  playback clarity that is motivating.
I also heard about SPL crimson and Audient interfaces which come with monitor control.But I'm tending to get an external monitor control ler if the AI does not satisfy my monitoring needs coz the AI will probably need replacement in a few years as part of the maturity process.

A lower cost interface may meet your needs (depends on your goals and the rest of your gear).
 
Generally speaking (as with most things), you get the fidelity you pay for.
Higher cost audio interfaces will have lower noise-floor.
You may or may not hear the 6-12dB difference difference on a stereo mix.
If you multiply the extra noise floor across 24 to 48 tracks of audio, it's suddenly a huge difference.
When using the interface with lower noise-floor, it's like peeling a veil of noise off the project.

Have a high-end studio with acoustic treatment and top-notch monitors?
 
Have savant-like hearing? 
 
If the answer is no to these questions, then I'd bet money you couldn't hear a difference between those units.  Get the one that you can afford and matches your I/O needs.
 
Now, it's a different story coming from an old or cheap interface to a modern one.  There's enough improvement in converter quality that there's usually a night and day difference in clarity.

I've been using a MOTU Ultralite AVB and it's excellent. I am extremely sensitive to latency and this unit just performs wonderfully at very low latency. 
It replaced my trusty Delta 66/1010 and the difference in sound quality was major, which to be honest did surprise me as I'm not one of those who are gifted with the ability to discern the converter chip model just by listening lol !

Jim Roseberry
 
Generally speaking (as with most things), you get the fidelity you pay for.
Higher cost audio interfaces will have lower noise-floor.
You may or may not hear the 6-12dB difference difference on a stereo mix.
If you multiply the extra noise floor across 24 to 48 tracks of audio, it's suddenly a huge difference.
When using the interface with lower noise-floor, it's like peeling a veil of noise off the project.

that is very true.
 
very impressed here how the MOTU 1248 sounds (or does not sound). I've almost completed rebuilding my system around two of these 1248s, improving all those little things that accumulated as ideas over the past 3 years (cabling, routing, ergonometrics, monitor mixing, etc) ... sound quality was more than acceptable before, but it's getting frighteningly clear, already at HP mixes in tracking with all these mics and external synths feeding the inputs ...

steveo42
I've been using a MOTU Ultralite AVB and it's excellent. I am extremely sensitive to latency and this unit just performs wonderfully at very low latency. 
It replaced my trusty Delta 66/1010 and the difference in sound quality was major, which to be honest did surprise me as I'm not one of those who are gifted with the ability to discern the converter chip model just by listening lol !

The noise-floor of the Ultralite AVB is about 7dB lower than the Delta 66.
Over the scope of a project (multiple tracks), there's no doubt in my mind that you could easily hear the difference.

Apogee Element could rule them all ...

The 2 headphone jacks requirement is ruling out a number of options.The babyface pro has 2 of them but the analogue outputs are only 2.Fireface ufx is out of my budget.I should probably connect another device to extend the headphone outs .

Make sure to checkout the MOTU AVB series.
The Ultralite AVB is an excellent audio interface.

I bought a Focusrite and loved it, but my laptop's FireWire interface stopped working with it after a firmware update and after a month of trying I never got it working so I returned it.

I use an RME UCX and split the headphone jack with a Y connector.

I picked up a quad pre to get me up to eight tracks on the UCX and then an Audient ASP 880 for the next 8.

I do miss the cool warm pres of the Focusrite. I'm thinking of getting one of those lunchboxes.

When it comes to noise floor, my physicist brother determined I didn't have any Mics that could test it because all my Mics had a higher floor. I don't know what RME uses to test levels so low but not cheapo Neumanns.