I just got a focusrite Isa one. I love it.

WSS

As to the Firewire interface, I'd say no.  USB is the way to go, since Thunderbolt doesn't seem to be catching on in the PC world.  If you are switching to mac, you would want to look at TB. 
 
RME and Lynx have very good USB drivers (the newest lynx interface is a pci card, tho).  RME has good hardware and excellent software and the new Motu stuff is right there with them.  An outlier you may want to look at is the TASCAM US line.  The 20x20 is USB 3 capable and gets down to 7 ms on my slower system (the only one w/ USB 3) and 11 ms or so for USB 2 on my better rig.  The 0-latency works great, however, for recording.  The 20x20 is good hardware and has a bunch of "pro" features you don't usually find on $400, 10X10 ADDA systems - word clock, ADAT, Spdif (which gives the 20 in the name) and a good software mixer etc. once you figure it out (and easier, in my opinion, than the Teutonic RME total mix).  The sound is good, close enough to the premium TASCAM UH-7000 that I switch between them without worry.  It is cheaper than the other units we are talking about and, in theory, should be well-tested with Cake software.  The new TASCAM hardware beats my old TC hardware, esp. the pres (and the TC hardware was better than the Presonus it replaced).
 
As if you don't have enough decisions to make already.
 
@

RME drivers are the standard by which all others are judged.
MOTU's latest AVB series is a close 2nd.
 
Fidelity wise, MOTU's AVB series is a tiny notch better than the Fireface UFX.
 
You can't make a bad choice between RME and MOTU's latest AVB series.
Both are rock-solid and yield low round-trip latency.
 
I've been running a Fireface UFX.
Most of the time, I leave it at a 48-sample ASIO buffer size.
Rarely (if ever) do I set it above 128-sample ASIO buffer size.
Absolutely glitch-free... rock-solid performance
 
After the computer itself, audio interface is the 2nd most critical choice for a rock-solid DAW.
Go with a proven top performer... 
It's an investment that'll last a decade... and you'll never give it a second thought.
 
 
 

I just saw an announcement for a new motu -
 
http://www.sonicstate.com/news/2016/09/28/new-motu-audio-interface/
 
seems to meet all the OP's criteria except 2nd headphone out, which is fixable.  $600.  And Jim sez MOTU fidelity is better than RME, which if true for this unit makes it a financial class winner - for the time being, anyway. ;-)

Appears from the responses , I will see a clear difference in sound moving from focusrite to RME or MOTU ?..

If we're dealing primarily with soft synths (with only occasional audio recording), are the differences between RME, MOTU, and Focusrite no longer relevant (or worth the increased price points)? 

when i got my rme babyface pro,
the very first thing i noticed,
was how on playback,
thru the same exact monitor system,
everything sounded a bit different to me.
 
more clarity.
 
i could hear where i had previously tweaked high end and low end, and now i didn't really like it.
 
smoothed it back out, and it all sounded more natural.
 
this i chalk up to the better DAC
 
so yea,
it matters.
no matter what the sound source,
the playback is critical.
 
 
 
the other thing i noticed,
was how neutral the preamps were in the babyface,
versus my two other preamps (and then into my older PCIe card)
 
i prefer neutral.
it lets me make 'mix' decisions much quicker and easier.
 
if i want 'highlighted' eq, or somewhat saturated, i can always go into my tube mic pres, and then into the babyface.
 
but i'm finding i prefer neutral,
and then eq to suit the mix, 
versus getting a bright track with a different preamp, one that i really didn't need bright,
but i'm stuck with that sonic fingerprint because of the nature of the preamp.
 

What Bat said.  It took me a while to hear the difference between Presonus and TC years ago, while I heard the difference immediately between the UH-7000 and TC.  Part of that is ear-training, too.  It can be easy to hear some difference, harder to tell which is better.

AT
I just saw an announcement for a new motu -
 
http://www.sonicstate.com/news/2016/09/28/new-motu-audio-interface/
 
seems to meet all the OP's criteria except 2nd headphone out, which is fixable.  $600.  And Jim sez MOTU fidelity is better than RME, which if true for this unit makes it a financial class winner - for the time being, anyway. ;-)

The larger AVB audio interfaces ($1500 and up) have newer converters and slightly lower noise-floor than the UFX.
Noise-floor is ~-117dB.
 
The Ultralite AVB and new Ultralite 4 both sound excellent at that particular price point.
Noise-floor is ~-112dB.
 

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.