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 :-)

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

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.

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!

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.

Just to add, it appears that the previously mentioned Tascam US-2x2 is also capable of standalone use, with an optional power adapter. For instance, if you wanted to play the keyboard through your monitors without starting the PC and/or Sonar.
 
From the Tascam reference manual: http://tascam.com/product/us-2x2/downloads/
 
9 – Standalone Mode
Overview
This unit will operate in standalone mode if it is turned on when
it is not connected to a computer by USB.
You can use this unit as a mic preamp and to monitor input
signals.
This function is convenient when you want to practice an
instrument without recording, for example.
However, when using US-2x2 in standalone mode, a TASCAM
PS-P520 DC5V AC adapter (sold separately), which is designed
for use with this unit, is necessary.

Settings in standalone mode
When operating in standalone mode, input signals pass-through
the built-in digital mixer and output selector, which are set at
fixed values, and are output from the output jacks. In addition,
when operating in standalone mode, the USB indicator will
blink.
 

Both have free shipping if you're a prime member at Amazon.
 
Focusrite is boasting low latency and the Tascam isn't...Amazon info I read.
 
Not knowing about either I'd go with the Tascam. It's cheaper, looks better and has an offer that could benefit you.
Amazon is great for returns for prime members-not sure if one isn't, so it's really not much of a gamble when you're not sure. Don't like it send it back and try the Focusrite.

husker
Sincere thanks to each of you for helping me out over the past few days on my questions.  This has been BY FAR the most helpful forum I have visited.  Quite honestly, you guys are the reason I will probably pull the trigger on Sonar.  
 
Now, I just need to decide which interface to use, Gen2 Focusrite or the Tascam US 2x2.  The Focusrite is newer and seems to get a bit better reviews, but the Tascam includes a version of Sonar I could use to get a cheaper SPLAT upgrade, and can be powered either USB or wall plug.
 
Again, thank you.

Tascam US-2x2 is $105 at Amazon (not including $40 for wall plug).  The US-4x4 is $195 including the wall plug.  Plus Amazon has a liberal return policy up to 30 days.

Is Sonar too much for a beginner ?? If I could start over and just buy Sonar instead of all the other stuff I bought, I would have saved many thousands of dollars over the long run.

Husker, it looks like you're well on your way. Here are my 2 cents:
 
You asked earlier if there were non-workstation keyboards with with lots of sounds. The good news is YES! The Yamaha S90-XS and the Roland Juno DS-88 would be examples of those. I'm sure Korg, Kurzweil and Nord all have their versions, too. Buying a "performance" keyboard over a workstation would probably save you $1000 or more from your total cost and you wouldn'y be buying redundant features. I have a Yamaha S90-ES (XS predecessor) that I only use the sounds for playing live. Otherwise it functions purely as a MIDI controller. FYI, I don't both with MIDI cables, just plug directly into my computer via USB.
 
The Tascam interface will work fine for you provided is works at all for you. I tried a Tascam a couple of years ago and it didn't work with my computer. Returned it for a Focusrite Scarlett and haven't looked back. Since the Scarlett isn't bus-powered (separate wall plug) and I don't turn it off I can sit down and play the Yamaha without the computer any time I want. I assume the Tascam has a wall-powered option.
 
So, I would start there and with SPLAT (what other answer did you expect from this forum?) I might have recommended Studio One but recent upgrades to Sonar have pushed it even to above everything else out there (don't even bother with Pro Tools). Add to this a decent set of powered monitors (KRK Rokit 5's are popular options - I own a pair and have no real complaints).
 
Later, when you want to add more to your system. I would look at an Arturia Analog Factory which will get you a decent MIDI controller with lots of features and a ton of analog modeled sounds to play with. As mentioned earlier, you can't go wrong with NI Komplete.
 
Good luck, have fun and keep asking questions!