Two keyboards/controllers instead of one

I currently have a cheap M-Audio Oxygen 8 which is only 2 octaves wide.  Good for browsing samples, but limited for playing.  I'm hoping to acquire a keyboard with a lot more octaves so I can play two-handed and use key switches.  I've had a regular wood piano all my life and I'm used to it.
 
Instead of buying an 88 key controller, I've been thinking of a 61 key controller (like the A800Pro) which would permit two-handed playing, but might be a bit tight for also key switching.  Can I use my Oxygen 8 for control keys and the 61 key controller for playing ?
 
I have a feeling doing so might also make a bit more sense ergonomically and functionally, or do you have to play the switches and left hand at the same time and having them close together is an advantage ?  Or does using key switches for expression limit you to playing the music with the right-hand only ?
 

 
Seems to me if both keyboards are sending on the same midi channel they could be seen by Sonar as if they were a single instrument ?
 
I'm really only thinking about the piano keys, not controller buttons and switches.
 
Mostly about using my Oxygen 8 for key switches though I'm sure I'll think of more uses for it.

 
Thanks FreeFryBertl, I just wanted to make sure.
 
Now if the canadian $ would just go back up.  The A800Pro is suddenly 100$ more than it was a month or two ago.
 

 I don't think you can combine two midi in devices to record the same channel at the same time.   

What TLW said, Each midi track can only select one midi input source at a time. 
If you were using real midi ( DIN) ports then you would need a midi merge box like a Yamaha  ymm2.  
I think the 2 midi track trick might work but I would think only the focused track with the input echo lit would be heard. 
 
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The different opinions pushed me to dig a bit deeper and I found the following in the X2 and X3 online documentation (I can't access for more recent Sonars, but I presume the text is unchanged) :
 
"You can also have multiple performers on different controllers sending MIDI data to either the same synth or multiple synths."
 
and
 
"To play one synth at a time from one or more MIDI keyboards
Since this is SONAR’s default behavior, simply use the UP ARROW or DOWN ARROW keys on your computer keyboard to choose the current track (the current track has a lighter track name background color), and use the Track Inspector or Console view to choose the synth you want to play by using the track’s Output, Bank, Patch, and Channel fields. With the default behavior, all MIDI input from all ports and channels is merged and sent through the current track. Notice that the track’s Input field says Omni."
 

Let me try to describe the whole picture:
 
The input of MIDI track in Sonar can either be ONE device or ALL devices (Omni). But not some subset of them.
 
Input MIDI is transfered to VST in case "Input Echo" is set. By default, it is in "Automatic" mode, so Echo is active on focused track and deactivated on all other. But Echo can be switched to "Always active" easily.
 
If we have E-Drum and 2 keyboards and we want control Drum VST and E-Piano VST.
 
1) if we play/record only one of these VSTs per time, we can set all tracks input to Omni and leave Echo in automatic mode. The data from all 3 MIDI sources goes to focused track (the result is recorded into one clip, independent from the device). We change the VST we control by moving focus (as already mentioned by keyboard, but also by mouse or with Control Surface plug-in by any particular (MIDI) keyboard key, controller or drum pad).
 
2) if we want control Drum VST by E-Drum and E-Piano VST by 2 MIDI keyboards simultaneously, we can not use Omni on ANY track since this track will use ALL devices than. So we need 3 tracks, one with E-Drum (only!) as the input and 2 for each MIDI keyboards with related Inputs (note that Global Omni is not the same as Device Omni, the last just means all MIDI channels from one device while the first means all devices). We also should force "Input Echo" always active for all 3 tracks. We set output from the first stack to the Drum VST and outputs from the second and the third tracks to E-Piano VST.
 
When recording there will be 2 separate tracks for E-Piano. It is possible to see them both in the PRV or just merge them (by MIDI bouncing the track with all (also overlapped) MIDI clips).
 
Note: when using Omni inputs, check that your VSTs have no "MIDI Output" enabled. VST MIDI Outputs are valid MIDI track inputs, so they can "leak" into Omny tracks! Example: if E-Piano VST has "MIDI Output" active and we use approach 1 (with Omni inputs). Initially everything is fine. But once we have recorded E-Piano and have switched the focus to the Drum track, E-Piano MIDI track data can leak throw E-Piano VST to our Drum track.That does not happened all the time, since most VSTs are not sending MIDI on the output, even when it is enabled. But once you get the effect, it is confusing.
 

I use this MIDI merger, which allows me to drive my VoiceLive Touch unit from two keyboards at once.
 

There are also 4- and 8-channel versions, the latter being a rack-mount. It's powered from the keyboard so no batteries or wall-warts needed. Just make sure at least one of your controllers can power an external device (one of my keyboards can't, so I have to make sure to plug the one that does into the In1/Power input).
 
This is just one of the reasons I prefer DIN connections over USB for MIDI.

I use 3 keyboards, an A-PRO 800, my old Roland XP-10 synth and AKAI LPK-25 mini keys. I have no trouble using two of the keyboards to extend the range, the LPK-25 is mostly used for key switches.
 
Depending on the VSTi even if the keyboards are set to different channels this still works if the input to Sonar and the VSTi is set to OMNI.
 
The A-PRO and LPK25 each uses their own USB connection and the XP-10 is connected via my Quad Capture MIDI port.