Yamaha P80 + ?

I like to hear your thoughts and experiences regarding this matter:
 
I used to have a Studiologic master keyboard connected to my AI but after almost 20 years it was worn out. I now use my wifes Yamaha P-80 digital piano - a decent piano with a really nice weighted key feeling. However, there are no controllers at all, so everything must be edited in SONAR afterwards. I like the weighted 88-keyboard for practice or piano recordings, but need something else when e.g. recording expressive/modulated Eastwest orchestra stuff. I think a 49-keyed controller will be enough for such recordings. Budget is around 300$.
 
The P-80 has no MIDI through, a controller like M-Audio Oxygen 49 has. Can I connect the P-80 --> Oxygen 49 --> Focusrite card and use both keyboards at the same time, or at least alter the keyboards without any change of settings?
 
The P-80 has a "...to host"-connection that, if I had understood correctly, could be connected to the serial port. If I want a keyboard without MIDI through (e.g. Alesis VX49 with the neat VST functionality) connected via MIDI to my AI, and the P-80 connected to serial port, will both be working properly in SONAR (latency etc)?
 
Another alternative is not to have another keyboard, just the controller part of it. Like Behringer FCB1010 MIDI Foot Controller, or Behringer X-Touch MINI. No sliders or wheels there, but actually I didn't like wheels control so a rotary control could do.
 
I'm saving to buy a RME UCX (with totalmixFX) so that's another thing to consider regarding a user-friendly controller well suited for the situation.
 
Thoughts? Any other ideas, solutions or hardware suggestions?

Cactus Music
I use a Roland A49 controller as I liked the feel of the keys compared to most that they had in the store. A lot of the brands are real cheap feeling. Yamaha, Korg and Roland have been making keyboards for a long time and those all feel real solid to me. I have a Akai Synth station 25 I picked up for $30 on sale and it's a toy. I can't really play it properly.   
Any how I like the size of my little A49 it fits on my computer side desk. It has the basic controller wheels as well as a very easy to use Tranpose system. You can send patch changes and stuff but I don't use those features , I could see it would be handy playing live. 
If you actually play a keyboard, you'll want it to feel right, just like a guitar. 

Good tip about the A49, I have had two Roland units earlier - both rock solid (D10 and JV-2080). I guess I have to use the USB connection in that case, if not going for Jon's idea about a MIDI interface.
 
Edit: And I saw it has the classic Roland wheel that D10 had! Still feel like I'm more used to that one vs the more common vertical one though I have had a Fatar keyboard since -97...

just to clarify - USB IS a serial port (Universal Serial Bus).  Maybe what you mean is that you wouldn't use an RS-232 port these days?

azslow3
I also will not use serial connections these days.
But why you want connect Oxygen (and alike, I mean modern controllers) throw Focusrite?

Just ignorance from my part. My hunch has been that USB is worse than MIDI and doubt of mixing USB/MIDI, glad to have that sorted out.

It should work fine on USB and keep Focusrite MIDI for P80. Some controllers will loose a part of functionality when not connected throw USB and some do not have MIDI at all. There is a rumor USB can be less responsive then AI MIDI, sometimes, something really does that (unclear what and when), but that is unusual.
Unlike ASIO Audio, all MIDI devices can be used in parallel, independent from the connection type.

Great! Will the USB keyboard work independently of the MIDI keyboard (and even at the same time - e.g. a 4-handed recording)?
 

Note about "knobs": controllers like X-Touch have encoders, while "simple" controllers have normal 270 degree knobs. Encoders are good for controlling the DAW and automatable plug-in parameters, since when you switch between tracks/plug-ins/parameters, you do not need to "catch" right position first, they are always in "sync" with current value. But for live controlling some parameter and "MIDI Learn" inside plug-ins (and so record changes into MIDI clip instead of track automations), encoders can be less convenient to use because of the "raster"/coarse resolution and no start and end physical points.

Good point. The X-touch is obviously not what I need.

From the A49 user manual, knobs, button, pedals and D-Beam can be assigned to control arbitrary CC or aftertouch.
What I have not found are either knobs are encoders or not. They look almost equivalent to the encoder on my A500S... but they are referenced as "knobs" elsewhere.
I would not like to control parameters by A500S encoder, it is perfect for choosing the program and can set the volume once, but it is tiny, has heavy turn and explicit "ticks".