It just does not sound professional.

I ran across this when I was floundering (and I still am!) around trying to make pro sounding recordings. 
 
http://www.resoundsound.com/best-mixing-tutorials/
 
It seems to me that people who make great sounding recordings typically acquire a great deal of experience making mediocre recordings before they do anything else. So I read the tutorials, read books, and record, record, record, mix, mix, mix. Progress is slow but it's also real.
 
You might also consider posting your music in this site's song forum to get feedback on your work. Great folks there!
 

No, a different interface won't make that great of a difference in sound quality if what you are getting now is completely unacceptable.  Native stuff is good to great and a professional tool, but if you aren't getting a good sound now it won't help that much either, I would think.  I'm not sure what soft synths come w/ Artist, but I've used most every Cake synth, old and new, and they all can sound good to great.
 
I would suggest it is a combination of things.  1st thing is to listen to your mixes across various systems.  Headphones are usually the last suggestion I would give for mixing, tho plenty disagree.  You are listening to raw sound w/ no interaction w/ air in the room pumped into your ear.  And your problem w/ the big stereo may be w/ that system and the room having bass problems (a common failing).  It may have other room problems, or the stereo may just suck.  You need to try out your mixes on various systems - car, mono bookshelf, computer speakers, a professional monitoring system that covers the sub woofer range.  It is like PR, even a bad system will help w/ your sound.  The point being is to learn your monitoring system by hearing how it sounds across other systems.
 
Then there is what used to be called arrangement (it still is but seems to be seldom talked about).  Balancing staccato sounds with something legato; lots o' bass needs salted with some high frequency ear candy, and so forth.  It is pretty much an instinctive thing, but it still needs to be cultivated and can be easily overlooked, esp. if you are working alone.
 
Finally, mixing is as much a skill as anything else music related.  I doubt when you first picked up a guitar or sat at the keyboard your playing sounded like you hoped.  I don't imagine why you would think recording and mixing would be any different.  It takes time to learn the tricks of the trade (or craft), but one has to develop an ear and experience.  You know how you want this instrument to sound and how that sound fits in the overall song.  Again, something that needs to be cultivated and develop an ear for it.  It might not be rocket science but it is a trial and error process and the less sustained work you can do the longer it takes.  And for the most part many home recordists are on their own (or have bandmates no more experienced) and have no mentors right there to learn from - which makes sites like these so important.  I read a lot of truths before I could hear and use them.
 
The good news is if you are primarily "in the box" you can work on all the needed skills at once, which will take a while but gives you total control.
 
Good luck

It takes a lot of patience, and well-recorded tracks to make a good mix. You might want to try some of the mix challenges that are available online. You can download pre-recorded material and mix it your self to practice your skills. There is a lot to learn about mixing before you'll start to get results that are audibly comparable to semi-pro or pro mixes.
 
Here's a link to an article regarding the mix challenges: http://www.soundonsound.com/news?NewsID=14319
 
Regards,
Dan
 

I don't own NI Komplete (wish I did) but if you are willing to shell out the cash for it's really a great package crammed with all sorts of cool stuff.
 
However... just having access to nice sounding synths and samples will not change the fact even great sounds need to be mixed and mastered properly to translate well to other soundsystems.
 
The synths and sounds that come with SPlat are really good and you can do a lot with them but you are on Artist, the base package that doesn't really have all the good stuff (mostly older instruments which are still good but not top notch compared to the fancier stuff).
 
You can upgrade to SPlat for far less money than Komplete costs and get those synths. They aren't as good as having Komplete but with some elbow grease and knowledge you can do a LOT of stuff.
 
BUT... again, you need to know how to mix those sounds and perhaps more importantly how to WRITE a tune in such a way it naturally sounds good before you'll get anywhere near pro results.
 
As far as samples? I really would not rely on the included loops to create anything epic. They're old and kind of busted. Plenty of sites out there that offer quality sample/loop libraries for free/low cost.
 
If that's REALLY your thing learn how to do your own sampling and looping. I think even Artist comes with some sampling stuff like Cyclone (and maybe the Matrix View). Groove Clip Looping is another area that avoids all the fancy sampler type stuff and allows you to do the same thing right in the Track View.
 
So... I'd say...
 
First and foremost use youtube search to find some general mixing tutorials or get a Groove3 monthly pass to learn about mixing fundamentals. You can ask mixing questions here on the forum too in the Techniques area. Tons of helpful and experienced pros down there.
 
Second, explore the tools and synths you currently have with Artist and how to tweak them. I'm not sure exactly what comes with Artist but it is a limited package so consider upgrading to Professional or better yet Platinum. This includes exploring FX which can have a HUGE impact on even crappy generic sounds. There are two vids by SWA/Karl Rose in the Cake store. One I think is called "Sonar X2 Workshop FX" and the other is "Virtual Instruments Revealed". They are great walkthroughs of ALL the synths and effects that were included in X2 Producer (almost all of which remain and only a few things have been really added so it's still relevant). Karl's "SWA X2 Complete" is up on youtube for general stuff.
 
When I first got started I thought I needed to invest in a TON of extra instruments and FX. Once I started learning how all the stuff I already had with Sonar worked many of those things became unnecessary. Saved me a fortune (that I don't have BTW).
 
Now I KNOW the things that are missing or maybe not as good as third party stuff and what's actually worth spending money on outside of the SPlat package.
 
Anyway... you get the point. You can do a lot more with some knowledge and simple tools than throwing a bunch of cash at expensive third party stuff and just poking away at it hoping something willl sound good.
 
Cheers.

I totally agree with what everyone has said so far on this thread.
 
Sonar provides you with the necessary tools to make GREAT recordings, you just have to learn how to use- them all.
 
Being blunt - if your songs don't turn out the way you want, it's not sonar's fault
 
One of the most important skills to develop is how to listen critically to everything you hear, whether it's your own recordings or commercial material.
 
Rip a few of the songs you think sound great and in the same genre that you're trying to emulate into Sonar and listen to them side by side against your recordings. CAVEAT: These commercial recordings will already be fully mixed & mastered so will be a LOT louder than your own stuff. Reduce the volume of your imported track(s) accordingly to gain a better perspective.
 
Before even thinking about investing in something like Komplete, I would seriously advise you to invest in a decent set of studio monitors so you can hear exactly what's going on in the mix.
 
Then at some point you will almost certainly require some sort of room treatment to try and eliminate (as much as possible) reflections, resonances, bass build up and suchlike from what is probably, not a good room for mixing and recording.
 
Above all, this is meant to be FUN so don't be put off at the enormity of the task ahead.
 
It's a long journey but the rewards are worth the effort you put into it.
 

One of the first things I learned when I got my computer and DAW set up years ago: It's damn hard to make songs that sound great, regardless of the genre. 
 
And I'm not even recording analog!  The only analog thing I have is a microphone, everything else is "in the box".  Still, getting the dynamics, EQ, arrangement, voicing, effects, etc is very tough!

One more thought about fat synths...the Z3ta sounds are pretty incredible ..just gotta sift through to find what you can use