So, I know the question is a bit strange. The bottom line is that I don't exactly have the time to find samples and synths that match the quality of the samples built into my keyboard.
Basically, my set up is:


1) MIDI out from PC into keyboard
2) Line Out from my keyboard (it has an actual jack for that)
3) Line In to my interface, Correction, 1/4in In, then out Line Out
4) Into my PC soundcard Line-In

The problem here is that a grotesque buzzing gets passed somewhere along the line. My question is this:
What is the highest-quality way I can record audio-output from my keyboard into my DAW?

What is the 1/4 line in for?  SONAR records the midi and then plays it back into the keyboard.  It is a sealed system.

To record the audio from the keyboard simply plug it into your interface in(s).  If you are using the on-board soundcard ... good luck.  It is probably mono (and you don't mention the keyboard) which might be causing problems.  But buzzing might be a ground problem, or a problem w/ the soundcard living in the computer.

So, you have to work the problem out.  Turn off keyboard and unplug everything from the keyboard but the audio out to the soundcard.  Does it buzz?  Turn it on.  Does it buzz.  Open the soundcard mixer and turn everything down.  Does it buzz?  Raise the level of the line in.  Does it buzz?

You just have to strip things down the basics and see what makes the buzz go away and identify the culpret.  It could be the soft mixer (likely) or a ground problem (which are usually 60 cycle hums) or something wired wrong.

@

Buzz could be as simple as a bad cord. 
John

What is the highest-quality way I can record audio-output from my keyboard into my DAW?

 
I have an 8-channel Yamaha mixer. The output of my interface goes to channels 1 and 2. The MIDI from the keyboard is connected to the interface. The audio output of the keyboard goes to channels 3 and 4. The "Always Echo Current MIDI Track" box is unchecked so I don't hear the MIDI and keyboard at the same time.
That way I can monitor everything from the mixer.
I don't use a lot of soft synths, mostly the keyboard's sounds. I disconnect the keyboard's audio outputs from the mixer and plug them into the interface once I've decided what sounds I want to use.
 

There is nothing wrong or unusual in using sounds from your keyboard.

I assume you are using your Casio WK-6500.

From the web site the outputs are.

Mic in

Audio in

Line output (L/MONO, R)

Headphones (standard stereo jack)

Sustain/assignable

USB: type B

External power (12V DC) * USB cable (A-B type) required to use USB terminal for computer connection

Can i make the assumption that the 1/4 inch in you refer to is you connection a microphone to the mic input of the Casio? If so what happens if this is disconnected?

A few thoughts of things you could try.

First and formost - the stuff AT has suggested.

Smoking gun in these types of scenarios in bad cables or connectors. It is worth trying a different cable as suggested by John.

Make sure you don't have any adaptors in the signal path.

I see the line out is L/mono R. I think this means there are two outputs on the keyboard. How do you have these connected?

If you are sending a line out signal to a mic input it could be too hot.

May be your audio interface is not up to the task.

davdud101


Basically, my set up is:


1) MIDI out from PC into keyboard
2) Line Out from my keyboard (it has an actual jack for that)
3) Line In to my interface, Correction, 1/4in In, then out Line Out
4) Into my PC soundcard Line-In

I find your description confusing. What is that interface mentioned in #three? If you have an audio interface, why are you connecting to
your PC soundcards line in? You say "1/4 in" so it must be an external soundcard, right? There should be no need to connect from it's line out anywhere, because the interface should manage all your sounds.

The noise may very well be coming from the synthesizer itself. Of all the synths I've owned over the years, the vast majority of them have had noise levels that are only acceptable for live use but pretty awful for recording. One exception was my old Jupiter, which had balanced XLR outputs and was very clean. The worst one I ever had was a Casio product.

Many synths feature S/PDIF connections, which is definitely the way to go for extremely low noise levels. But if you don't have that and must record from the audio outputs, you're just going to have to mitigate the noise problems after recording. Use slip-edits to trim clips so they start right at the start of signal, use short fades at the start and end of the clips. If it's really bad you might have to use volume automation to kill the noise during gaps in the audio. Recording hot won't help, as the noise is coming from the final amplifiers in the synth and turning up the volume turns up the noise, too.

If you're getting hum (or buzzing) from the synth it's probably a shielding or grounding problem. It might be worth taking it to a knowledgeable technician to see what can be done about it. It could even be a loose ground connection within the case. More likely, it's just a bad design in the synth. I've seen power transformers located right next to I/O jacks; not much you can do about that, but a tech might offer a useful opinion. 

This unit uses an external wall-wart power supply, which are often hum sources, too. They're typically not well-filtered and poorly grounded. I'd be inclined to try a higher-quality aftermarket 12VDC power supply. Or, if you do take it to a well-equipped technician, chances are he'll have a well-filtered variable-voltage power supply you can try out.

Thanks for the replies, everyone! Regarding my 'interface'... It's actually an analog interface- the Roland BOSS BR-532 'portable digital studio'. Can't say it was really designed for this, but it sounds awesome, works as a preamp for my Line-In.

Buzz as mentioned can come from a number of sources....

Bad cord

Incorrect cord... if it has a stereo output, get a stereo to (2) mono outputs and plug in the 2 mono's to the inputs on your sound card.

Power supply: as Dave mentioned.... the wall wart could be to blame for the buzz...so, since the keyboard will run on battery power, run it on battery while you make the audio recording part. Batteries put out "pure" DC whereas the wall wart puts out DC with an embedded AC due to the poor filtering in the tiny wall wart power supplies. That AC can easily make it's way into places you don't want it.