OldNick
You can only tell me I have it "wrong" so much before I say "well it ain't me"...gotta do this...gotta do that...nup. This programme is supposed to serve me...not the other way around.

A program can serve you only if you learn how to tell the program what to do. It can't understand what you want without input that makes sense to it, and SONAR is no exception.
 
Granted, sometimes it's complicated to specify everything you want it to do. But a compensating factor with SONAR is once you figure out what you want it to do, you can often save a preset and never have to think about it again.
 
One day I sat down and created about a dozen export presets that cover all my needs. If all the options hadn't been there, I wouldn't have been able to create the various presets. But I haven't had to deal with the export menu since then, and all the exports are flawless.

OK.One thing here...well two.
 
Export is fine. The level is a little low, but only about 3dB or so.
 
It's the mixdown that is the problem. It's not just different, it's disastrous. I am talking -20dB. ANd AFAICS all the tracks  I want to use are set up with the same routing (Master) and none of them go into the red. Some of them are pretty high in peaks, but as I say an Export does not collapse the way the mixdown does. 
 
Everything is pretty complex here, for a newby, but I swear I have had tracks behave differently between one mix and the next and I have made no changes. I now bounce tracks one by one to see which is causing trouble and I swear they change.
 
Bottom line. If I export, it's fine. If I bounce it's useless. I guess in the digital domain I just normalise after bouncing, but if I can't trust the mix.
 
I did address all the ideas expressed by Bristol_Jonesey, as best I could

_I_ think it has a lot to do with what is muted and soloed etc. I have done a track-by-track and found a silence mixdown of certain tracks if they are not "right"...not soloed or muted etc. I feel that is WRONG.
 
I am not getting the tiny little output I was getting from mixing down any more and I have NO idea why.  I can't even route my audio-based tracks to Master any more. It's not there. New project. New tracks. New synths. No Master Output available.I can only route to my output hardware. Done nothing I know of.

You have to insert your own Master Buss if starting from a blank project.
 
SONAR doesn't do it for you unless you start from a template which already has one.

yeah but it was there in the fle I was working in and I never asked. It was suggested as a soilution. In fact when I trieda new fil;e  and Froze and then Bounced, it worked better than the old CWP that ghad the option
 
Not happy....very confused

The thing is, I had better results with mixdown when Maater was NOT available than wha it was. The mixdowns were fIne. 

When faced with a mystery such as this, I like to back up and break it down into the basics. So let's start with some basics, and I sincerely apologize if it's so basic as to be insulting. But it's a computer; in the end it all comes down to the simplest of concepts, e.g. 1 + 1 = 2 (or 1 + 1 = 10 if you think in binary).
 
"Mixing" in a DAW is all about basic arithmetic, specifically addition and multiplication. With four frozen tracks, no active plugins or volume automation and faders at zero, a bounce or export is going to be literally the sum of every sample in the source tracks. Nothing is random, so each bounce or export will produce exactly the same results.
 
Normally, we route each track to one or more busses, also known as "mix busses" because a mix is a summation and the bus is where the result of said summation ends up. Think of the DAW as an adding machine (if you're old enough to remember adding machines!) where each track is a numerical entry and the bus is the final sum. As long as the numbers remain the same, the grand total will also remain the same - every time you add them up. 
 
Freezing, bouncing, exporting and routing to a mix bus all use the exact same summing process. The only difference is where the sums end up. This is why the mix sounds the same whether listening to the master bus or listening to an export: the math is the same in either case.
 
So if the math is always the same, how is it possible to get inconsistent sums? Only one way: changing the source data. Going back to the adding machine analogy, if you were an accountant and your sum came up a dollar short of what it should be, you wouldn't assume the adding machine was broken. You'd look back over your inputs and see which one had been incorrectly entered. Similarly, if a bounce sounds different from an export, then it couldn't have been the same data that got summed.
 
First rule: always use a master bus. Second rule: make sure everything goes through the master bus. Everything. Verify that by muting the master bus - everything should go absolutely quiet. The bus in turn should always be routed directly to your audio interface. IOW, the only way anything gets to your audio interface is through the master bus. 
 
Now you have a dependable reference. The sound you hear during playback is the sum of every track routed to the master bus. That's exactly the sound you should hear when you export the mix or bounce the entire mix to a track. If an export or bounce ever sounds different from that reference, then you have made a mistake.
 
How many ways are there to make such a mistake? Too many to enumerate, unfortunately. Just when I think I've found them all, a new one arises to bite me in the arse. But the best preventative is to establish a procedure and then consistently stick to it.
 
For starters, I'd suggest that bouncing multiple tracks to a new track is almost never needed in the digital world. If you want to treat 4 tracks as a single sound source, route them all to a bus instead (which in turn is routed to the master). Then you'll be able to adjust their collective volume with a single fader and to apply a single set of effects to all of them as a group. If you want to combine them into a file, perhaps to import into another program or project, then just solo the desired tracks and do a normal export. As long as it goes through the master bus, it will sound exactly the same as when you were previewing it.
 
I'd also suggest that normalization is also rarely needed or desirable. For setting the ultimate perceived volume, use a limiter on the master bus. It's perfectly acceptable for a raw mix to have an average RMS of -20dBFS. A separate step called mastering is used to raise the final level to the desired target. Mastering is quite different from the mixing process, and in the professional world is a separate, specialized discipline all its own. For us DIY mortals, it's basically an EQ, a compressor and a limiter on the master bus and lots of trial-and-error until it sounds good.
 
Sorry if this was overly basic, but it's really all about the basics. Also sorry about the rambling stream-of-consciousness brain-dump. It's still early over here on the other side of the world.
 

Excellent post Dave. 
 
I'm confused by a few terms the OP using. I get Export but the tem "mixdown" is a little strange to my way of thinking with in a DAW.
The "mixdown" is the export.
We hear the mix via the master buss.
Soloing tracks is not involved in a mixdown. Solo is used to listen without distraction to any given track, synth or sub mix buss.  
 
I understand some people like to bounce a song to a internal "mixdown" and I see this might be what your having issues with. Not the export mix>  So is this the issue? you can't seem to get an internal bounce to sound right? 
 

Might have dim solo activated and a hidden track soloed.
(longshot)

An alternative work flow is to bounce tracks internally (select the tracks and bounce to track(s) with appropriate choices in that pop up). Then verify that bounce and drag/drop that wav file out of SONAR or into the browser.

As mentioned above, a wonky export is routing, export choices, or a combination.