In a track, there is a volume slider you can move with the mouse:
 

 
In this image, the volume of the MIDI track is (101), in the audio track it's 0.0. Move those sliders to change the volumes.
 
Or you can click Views at the top and select Console to bring up a Mixer view like this:
 

 
Here you can easily see all the volume settings and change them if desired.

What a lovely thing for you to do!  Thank you.  Just out of curiosity - what program were you using?  I did not know to do that because when I had the old Panasonic with a mic on a towel on top of it, I didn't have to!  Therefore, I thought that I could simply record the 2 tracks without any fuss, switching from audio to MIDI. 
At your suggestion, I recorded an audio track at 30 on the receiver.  That's the norm.  Now in order to record the MIDI flute while listening to that track, I had to put the receiver up (40-42) and then go in to console and back the audio track down so they would be equal.  This worked, altho I have to be very careful or the receiver drops out.
So now I do have a way to do it.  What has surprised me all along is that the keyboard instruments are so faint unless I turn everything way, way up.  Its volumes and the receiver's.  Doesn't seem right, somehow.  For example, I could never do really loud drums (which I can hardly imagine would come up in this work!) because the receiver would "protect" and quit.
It just never occurred to me that one would have to do it this way, b/o previous experience.
So thank you!  I can get along this way.  Sister

Hi sister - sorry, I didn't mean to get irritated.  Yes, I do remember you from years ago.

Ok, first, another question - you said the piano is not acoustic, and not connected to anything.  what exactly is it, then?  (and we may be just getting stuck on "terminology").  an "acoustic piano" is any piano which has to be tuned by a professional tuner, like uprights or grands or baby grands, etc.  is that what your piano is?

now, to adjust the levels on your MIDI and piano tracks look at these pictures below.



first, click on the number for the audio track to select it.  then use the slider to reduce the volume of the audio track (your piano)




then click on the number for the MIDI track and increase the volume of the MIDI track by raising the slider .



now you can adjust the overall volume of both tracks mixed by adjusting the MAIN slider.

Dear Beagle,
That is so nice.  I have printed out all examples.  Yes, of course you are right.  Every time someone said acoustic, I immediately thought electronic, as evidenced by one of my answers.  For no reason at all!
Before I leave you to, no doubt, help others as graciously and unselfishly as you have me, (why, why didn't I ask you guys 2 years ago?), just a couple of unimportant queries:
On the MC5, if one does Track>Properties>Volume (which was one of the ways I was trying to solve my problem), one is presented with a +/- box with a 0 in it.  One can only go +, obviously.  So one adds something, plays on the track, nothing changes and the box is back to 0.  Just curious.  It really doesn't warrant digging in to.
When I finish a track, I export it to My Music and Windows Media Player.  I can then add it to a playlist for a cd.  Very simple.  What is the best way to export together the 2 tracks?  One hears them together very nicely.
Again, thank you all for all your help.  You can't imagine what it means afer all this time!  Sister

Sister Maria,
I looked at the volume thing and also realized that if you're using MC5 then it's different than MC6 and the screenshots I gave you above are for MC6.  if you're using MC5, then the volume is adjusted by a slider, but it looks very different than MC6's sliders.

in MC5, open the properties of the track you want to adjust by clikcing on the little down arrow: 

 
 
 



then use your mouse to click and drag the volume up or down on the volume slider: 

 



as far as your question:  the TRACKS>PROPERTIES>VOLUME
DOES do the same thing as above, but it looks very different and the numbers are very different.  0 = OFF and 127 = highest possible volume (+6dB).

personally I wouldn't use the volume that way, it's unintuitive to me, but it does still work.

Hi dear,
Yes, I had found and messed with that before.  I hadn't examined the console view at all, which works.  Like you, I won't use that Track>Properties>Volume thing because, as mentioned, I would increase the #, go back to the track, find no difference, go back to see the # was back to 0.  Doesn't matter. Don't need it, was just curious.
What the whole problem ultimately boiled down to was all of you showing me how to separate the tracks and their volumes. 
I still find it odd that volumes for the keyboard have to be turned so far up for some instruments, that the receiver drops out.  I am not hard of hearing, the volumes would not be considered excessively loud by any stretch, matching the piano track which  is much, much lower.  I can still manage just fine, thanks to you.
I did keep MC6 on my computer.  Had been told it would work better with Windows 7.  It made no difference.  I'm used to 5, but may use 6 sometime just for fun and a change.
Is it nice in Texas?  I'm way out on a point in downeast Maine.  We've had snow, but as I look out I see that the bay just below the window (tide's out) has lost its ice because the last 2 days have been so warm!
Do keep in touch and thank you for your thoughtfulness and generosity.
Sister
 

Odd, isn't it?  The keyboard's volumes have always been up as far as they will go.  As stated before, the only place I seem to be able to control volume noticeably is on the Sony receiver (STR-DH100).  This goes up to 70.  I record the piano at 30.  The music I am transcribing is quiet. Let's say I choose trumpet for a MIDI track.  At 30, it is barely discernible.  I go in to MC5, as you showed, and push it up to 6, its maximum.  Not much difference.  I go over to the receiver and push it up to 50.  Then it's audible.  Of course, I then have to go back in to the piano track and turn it way down.  Too, as I have said, altho I haven't done this often, the receiver will drop out protectively if I'm trying to record the MIDI with the audio. Can't handle it, I guess.   
However, you have been way too kind to use your time, and I can get along now  if I choose the instruments and try to balance carefully.  If I were a rock band, or wanted noisy drums and horns, etc., ....?Which, since I don't, doesn't matter. 
You are a professional musician?  Band of some sort, or solo?  A beagle singing?  Do you have a beagle?
Windrow Sanctuary is a wildlife sanctuary.  I am a Franciscan Sister.  Have 3 rescue animals:
Abbeycat, who lives in the oratory;  Katy, a mixed breed; and Chief, a Belgian draft horse.  I was asked to take the Belgian as he was near death from abuse, starvation and worms.  He is now healthy and very happy.
I appreciate all the attention you have paid to this problem.  Blessings upon you!  Sister
 
 
 

I have no doubts, sister, that if I were in the room with you we'd be able to figure it out in 5 minutes and say, "well that was obvious!"

but I must admit that I don't know what else to try at this point.

You are a professional musician?
No, an amateur.  I play keyboards in my church band and I sing and sometimes lead worship
Band of some sort, or solo?
Yes - see above! :-)
A beagle singing? Do you have a beagle?
I do not have a beagle and haven't had one since elementary school, but "Beagle" is my nickname.  It was given to me at a time when my life was very different than it is today!  Most of my high school buddies still call me "Beagle" exclusively.

I do love beagles, tho, they're great dogs! 

we currently have a Miniature Pinscher and he's a handful!  His name is "Scooby"

I'm glad to hear you take care of rescue animals.  that is a noble cause!

Blessings to you Sister!

Maria.... part of the problem is we can not see what you have and what you are doing.  

One possible solution would be to have a friend or yourself make a short video zooming in on the inputs and outputs and where cables go and show all the gear, so perhaps we can make some sense of it. A phone can do the video recording easily. 

The video can either be uploaded to youtube (free and easy) or loaded to a site like dropbox or box.com and the link shared. That way, maybe we can see exactly what you're doing and offer the best advice to a remedy.  

Like this>>>  http://www.youtube.com/watch?v=3-OMoe9f8eI

just a thought.