The lists of possible culprits I provided is provided to point out what to troubleshoot. Not saying your amp is definitely the problem, but it was a logical possibility. So, you ruled out your amp. Good. Proceed further.
 
Since you have connected directly into the audio interface, do as jungfriend says: record the guitar clean. If the clean recorded guitar is OK, keep it clean on a track by itself, now add the overdrive. If you get the undesired distortion again, you have your culprit, the overdrive itself. If that's the case maybe you can try using a plug in that works better for you with an overdrive effect or virtual amp that has the overdrive sound.
 
Decisions, decisions.
 
If you feel it's the audio interface that's just not a good carrier or handler of your overdrive effect, the only way you can troubleshoot what you suspect to be a bad audio interface is to use another audio interface.
 
 

The only problem is that I used to be able to record my amp with no issues whatsoever - or even record with the POD.    I don't like the choices given me for plug-ins with overdrive, as I like the Dumble tone.
 
I don't see why I would have to give up recording with my amp.   There has to be a solution somewhere, as people do record amps.  
 
I may have to get another interface.
 
Thanks!
Greg
 
 

Before buying another audio interface, I hope you feel you have exhausted all other troubleshooting steps that might get you the desired results. 
 
I know you've been recording for years, yet when recording the amp are you sure using another mic or repositioning the mic wont help?

Thanks for at least replying to everyone, You would be surprised how many people come here for help and don't. Sorry this is driving you nuts.. I bet I wouldn't be an issue if you were using a 16 Track Reel To Reel and a cheap mixing board. This modern equipment was designed to frustrate the most technically savvy person and always be on the edge of failure. The price we pay for accessible, inexpensive recording gear.  
Reading your posts I'm starting to lean towards the software that goes with the interface.. This so called "auto sens". So are there any other quad capture people out there? we need to hear your opinions. 

Did you check the mic distance as I suggested earlier?

thomasabarnes:   I've used 2 different mics and have tried positioning them in different places.  Nothing has helped.
 
Cactus Music:   I like things simple, and this stuff certainly isn't simple - not for me, anyway. 
And I try to answer everyone because I asked for help - and I appreciate it when someone offers.   :)
 
thebiglongy:  I saw a video on how to position the Sennheiser e906.   It said to lay the mic right on the front of the cab.  I actually put it about an inch or so away.   It doesn't help (near, far, makes no difference).
 
Thanks!
Greg

Greg,
Its proabably time to take a step back and try a different approach to solving this problem.  Can you list out your entire signal chain, including your routing in Sonar (sends, busses, plug-ins, etc.)?
 
There is an explanation for what is going on and we can find it, but it may require a more systematic approach.

HI Greg54,
 
You said:
"I was running my guitar into the amp with no pedals, using only the amp's OD.   So I decided to use a POD today and go direct into the interface.    I also turned on the Auto Sens on the Quad Capture to see what that would do, and it caused my signal to overload, even though my volume was set lower on the interface.   Isn't the Auto Sens supposed to keep that from happening?
 
Anyway, the OD with the POD direct was the same as with my amp.   So the issue is not my guitar amp."
 
Okay, rule out the amp. As an aside, a very useful technique for guitar recording is reamping. You record a clean, dry, direct signal into your DAW, then you send the recorded signal into an amp and bring it back into the DAW on another track. This way you have a reliable signal to start with and can route it to a variety of amps, effects, dongles or whatever you like without losing the good track.
 
The POD is a dongle. It also is an interface. When you plug into the POD you are adding another step in the signal chain. Try going direct into the Quad Capture. Also disable auto sens; enable auto sens. See what happens with both settings.
 
Good luck,
Paul

I went looking for that auto sens feature and it appears that it is simply setting levels based on the highest peak it sees during an "evaluation process" (when first pushed). After that, if you play louder, it may very well clip. Many plug-ins also have this feature, and the best way to use it is play an open full G as hard/loud as you can when it is doing its evaluation. After that point it should not clip with "normal" playing, since that hard full G should be louder.
 
That is something to check with that interface, but it also has a clipping indicator on the front of it (and within its GUI/control panel). That control panel should be registering the clip that it is passing into your computer. If it is not (either on the interface or its control panel), I would highly suspect the interface. Check all of those parts first.
 
Also, *if* the interface continues to be a suspect, most places have a 30 day return policy, so you can talk to them and be upfront and say you have a suspect interface and want to try another just to check things (and then return it if not an issue). Many places would not have an issue with this. But be sure to thoroughly check your interface now first. From things you have said, the only changes from "working signal flow" to "non-working signal flow" are external to that interface... and the "buck stops there."

dwardzala:    Right now I'm recording very simply.   I am using no effects or buses.   I put those in when I mix and master.    Plug-ins are Toontrack EZKeys and some keyboards that came with Sonar X1.
 
jungfriend:  "You record a clean, dry, direct signal into your DAW, then you send the recorded signal into an amp and bring it back into the DAW on another track."   
Although I've been recording for a few years, I have not gotten into a lot of techniques.   So this is above my head. 
 
I have tried Auto Sens, and mettelus just explained to me how it's supposed to work.   I guess I was doing it all wrong.  However, I would pretty much bet that it's not going to solve the problem.
 
mettelus:  Thanks for explaining that to me about the Auto Sens.   :)
I have had this interface for about a year.   This is a new issue.   It didn't use to do this.  So I'm baffled.
 
Thanks!
Greg