Another thing that this thread shows is that a modern DAW is powerful and complex enough to be everything to everybody.  So you have opinions from musicians, engineers, producers, sound designers, hobbyists, etc.  And that's all good. A lot of great knowledge and opinions were shared. That is the great thing about the diversity of these forums.
 
But ...
 
It sort of reminds me of the story about the elephant and the blind men. It is a story of a group of blind men (or men in the dark) who touch an elephant to learn what it is like. Each one feels a different part, but only one part, such as the side or the tusk. They then compare notes and learn that they are in complete disagreement.
 
Regarding his needs - the original poster stated that he was a former piano player and wanted to get back into playing, maybe with a workstation.  He is mostly interested in synthesizers and sounds, using 88 keys.  He has already demo'd some gear at his local music dealer.  His DAW interests are mainly with the instruments and effects. No microphones, or external instruments, other than a keyboard synth are planned.  He has already downloaded the trials of several DAW's.  He did not seem to mention recording and mixing among his current goals.  The question regarding sound interfaces becomes relevant if virtual instruments or live effects monitoring are important. 
 
His original question was whether Sonar was too steep for a beginner to use. 
 
As Craig said earlier in the thread, it is like purchasing your first musical instrument. You should get the best you can afford, and grow into it as you learn.
 
If you get Sonar, there will be plenty of folks here to answer your questions :-)

I guess I really have derailed my original question.

husker
I guess I really have derailed my original question.

No, it's nothing to do with you!  Keep pounding!  Success awaits you!
 
You just asked a loaded question to a highly diverse, opinionated, well informed group of individuals, who each approach their tools in a way that works for them.
 
The more you learn, then the more you can narrow down the scope of a question or a problem.  The broader the question, the broader the answers will be.
 
Trust me, we were all in your shoes once, LOL!!!  I have learned a lot from these forums over the past 20 years.

husker
So, considering a keyboard with a midi out and two TS 1/4 outs (L and R), and an audio interface.
 
A.  I would plug the midi out of the keyboard into the midi in of the interface.  
B.  I would plug the L 1/4 of the keyboard into input one of the interface (using some cable that is 1/4 to XLR/TLS)
C.  I would plug the R 1/4 of the keyboard into input two of the interface (using some cable that is 1/4 to XLR/TLS)
D.  I plug the monitors and headphones into the interface.  If I want to play the keyboard without the computer, I just plug them into the keyboard, since the interface requires USB power.
 
Am I correct on the A,B,C,D?
 
In this configuration, I am unsure on why I would need to plug the USB out of the keyboard into the computer to play or record anything.  The line outs and midi out of the keyboard into the interface takes care of this, correct?  
 
*I understand that the the keyboard may have specific software for programming that would require this connection.

I also consider US-2x2 (for different interface the answer can be different). In general, everything is correct... but with small corrections:
 
A. you will need 2 MIDI cables (2 directions). Or you can use one USB cable instead (just for MIDI in this setup, there is no limitation how many different MIDI inputs/outputs are used simultaneously and either they are coming from the same hardware as audio)
B. and C. US-2x2 has combo jacks, fro XRL or TS or TRS. So you will need 1/4 to 1/4 cables, not 1/4 to XLR
D. US-2x2 can run in standalone mode, you will just need a power supply for it (so it works with the computer switched off). No need to reconnect monitors then.
 
But I repeat one more time. As already mentioned by Abacab, you do not need that extra interface in such setup, even in case you get it.
 
@abacab:
People here have understood the original post, the background and wishes. And it looks like I am not alone who with the same background and the same wishes has started to use Sonar several years ago. And so people mention how these wishes and setups have changed over time. Not to force anything, just for information...

azslow3
 
If you really go MOX/FA way , lets make it clear - you do not need another audio interface. For other you can check either it has build-in interface (not all DPs have it).

I found some more info regarding the Yamaha MOX and the internal audio interface.  ...
 
This approach seems to solve the question of "how to play the keyboard with the PC or Sonar turned off".
 
From a review at SOS: "Sonar's audio output appeared in all its glory at the MOX's stereo output jacks."
 
So you just hook up your studio monitors or amp & speakers to the audio outs from the MOX.  The keyboard provides the audio outs for either standalone or DAW use.  Clever!!!
 
http://www.soundonsound.c...ticles/yamaha-mox6.htm

Reading the replies that you have conceived, I think everybody has a point. You are the only one capable of answering these questions. Is this enough to make you wanna choose SONAR?
I think the amount of answers, and the interest, could be enough to to make you think about it.
This is an unique forum with regards to the response / feedback / feedback you'd get from a "regular public" site.
You, and only you can will know what you need, in regards to plugins, features and "extras". 
I wish you the best of luck, either way.
All the best.

I think husker has figured it out pretty well and his A, B, C, D all work out. I would also be inclined to agree with his assessment that a dedicated interface is better, even if the workstation provides a few options. No workstation I know of save the Korg Oasys offers phantom power on the inputs for instance, so if vocals or guitar are ever going to be recorded with a studio condenser mic that would be an instant (obviously ultimately solvable) issue. Also, you could take the laptop and interface to the couch, on a trip, whatever, and still work with headphones in high quality.

husker
I guess I really have derailed my original question.

Maybe so, but I think you started a very interesting and valuable thread that encouraged lots of good discussion. The information here will be helpful to many others as well.
 
I think abacab made a great point with "The more you learn, then the more you can narrow down the scope of a question or a problem." To that, I'd add the more precisely you can define what you want to do with computer-based recording, the easier it will be to choose the path that accomplishes you want to do.
 

azslow3
 

I also consider US-2x2 (for different interface the answer can be different). In general, everything is correct... but with small corrections:
 
A. you will need 2 MIDI cables (2 directions). Or you can use one USB cable instead (just for MIDI in this setup, there is no limitation how many different MIDI inputs/outputs are used simultaneously and either they are coming from the same hardware as audio)
B. and C. US-2x2 has combo jacks, fro XRL or TS or TRS. So you will need 1/4 to 1/4 cables, not 1/4 to XLR
D. US-2x2 can run in standalone mode, you will just need a power supply for it (so it works with the computer switched off). No need to reconnect monitors then.
 
But I repeat one more time. As already mentioned by Abacab, you do not need that extra interface in such setup, even in case you get it.
 
@abacab:
People here have understood the original post, the background and wishes. And it looks like I am not alone who with the same background and the same wishes has started to use Sonar several years ago. And so people mention how these wishes and setups have changed over time. Not to force anything, just for information...

Was not trying to single anybody out for lack of empathy.  Just my attempt to cushion the "brain dump" for a beginner's perspective.  In fact, you provided some really useful info!

husker
As I said, I have no experience whatsoever with DAW or recording, so I have a "clean slate."  

Do you know anybody who plays with this kind of stuff? I was in a band back in the turn of the century and learned from a guy who was helping us record our demo. He had DP 2 or 3 and he gave me the disk to install on my laptop and I basically sat at his elbow and watched him work.
 
I use Reason a lot with Sonar and while Sonar is my main piece of software, I can't recommend Reason enough to beginners. the downside with Reason is that they closed their forum and so a great resource was lost.
 
I also don't know if you need a keyboard workstation if youre just starting out. you'll end up with a lot of duplicated functions that you'll never use on the keyboard. obviously you want a good keyboard feel, but it seems like a huge outlay for a "beginner"
 
EDIT TO ADD: sorry I see you're set on the workstation (and for a sound reason).