I have a Yamaha YPG-635 and I have SONAR 8.5 and I want to connect the keyboard with a sub cable I have. I also want to record audio with a condenser mic. Should I get a solo audio interface with one input and connect the keyboard to my computer with the USB cord, or should I get an interface with two inputs and connect both the mic and keyboard to the interface (if this is the case do I need a different cord to connect the keyboard to the interface). Also, is it better to get a USB audio interface powered by USB or powered by phantom power? Thanks

StevieG
I have a Yamaha YPG-635 and I have SONAR 8.5 and I want to connect the keyboard with a sub cable I have. I also want to record audio with a condenser mic. Should I get a solo audio interface with one input and connect the keyboard to my computer with the USB cord, or should I get an interface with two inputs and connect both the mic and keyboard to the interface (if this is the case do I need a different cord to connect the keyboard to the interface). Also, is it better to get a USB audio interface powered by USB or powered by phantom power? Thanks

As you've suggested, it is possible to hook a Yamaha keyboard up the the PC via USB for midi purposes. You can record midi into Sonar and have sonar play midi out to the keyboard. If your Yamaha keyboard is anything like mine, there will be some programs that are restricted to the keyboards front panel and not available via midi. 
 
If you want to record the audio from the keyboard though, you'll need an audio interface, although you might just find that taking midi from your keyboard into Sonar and then patching into virtual instruments will give you more options than your keyboard's sound engine alone.
 
Get an interface with at least two microphone inputs. Stay away from anything that is USB bus powered - it's not likely to be a quality product.
 
 

Would Focusrite Scarlett 2i2 USB interface work- it has 48V phantom power? .....Also do you know the basic steps for setting up my keyboard in SONAR once I've plugged the USB connector into my computer? I tried to follow the steps given on the cakewalk support page, but I got lost at some point.

I suppose the 2i2 would work, although it is bus powered.
 
It's been awhile since I've had the keyboard hooked up via USB. If I recall correctly, you use the keyboard's front panel menu to set the keyboard in PC mode. Take a look at your owner's manual. You can also try the forums over at the PSR keyboard site, they cover many Yamaha keyboards.

Alright I'll check that out thanks man

One of the primary issues with buss-powered interfaces is providing phantom power to condenser mics (generating the +48V level with minor current requirements). Many struggle to do so. Look for one that offers a choice (AC-powered in addition to buss-powered; or AC only). The Tascam US-NxN series is great. I have the 16x08. The 2x2 has the same great mic pre-amps. It also has an input for optional AC power.
 
http://tascam.com/product/us-2x2/

TheMaartian
One of the primary issues with buss-powered interfaces is providing phantom power to condenser mics (generating the +48V level with minor current requirements). Many struggle to do so. Look for one that offers a choice (AC-powered in addition to buss-powered; or AC only). The Tascam US-NxN series is great. I have the 16x08. The 2x2 has the same great mic pre-amps. It also has an input for optional AC power.
 
http://tascam.com/product/us-2x2/

The problem with USB is you have only a few watts to work with. You can convert 5v to 48 volts, you just lower the available current by a factor of 48/5, and that's not even accounting for all the other circuitry that's drawing power.