It's hard to know what to suggest here. You say that PIP is switched on. The DR05 has a wide input range encompassing both mic and line levels, so it shouldn't overload easily. Have you set the DR05 to its minimum gain setting, (not auto gain) ? With rec light flashing, hold << button until you get to minimum (Sorry, I can't remember the way it's displayed!). Does the problem still occur?
I just looked at the specs of the CS10 & did a back-of-envelope calculation. Sparing you the details, as the CS10 is a low output mic, when it's coupled with the lowest sensitivity of the DR05 it should allow for a sound level of about 130dB before clipping! So the chances are that the mic itself will overload before it overloads the input of the Tascam. Or, more likely, it will run out of power from the PIP output - This might well be what's happening as it's a common occurrence at loud shows, hence the use of battery boxes.
But, I'm thinking that your street ambiance isn't likely to be that loud unless you have an emergency vehicle pass by, or they're excavating the road with jack hammers, etc.
A strong possibility is wind / air movement. The CS10s have no protection against wind whatsoever. Outside, even on a still day, a large vehicle passing close by creates sufficient air movement to overload an omni mic such as this. The result will be clipping & heavy distortion. The overload in this case could be in the mic or the recorder, it's hard to tell. You could try the Tascam's low pass filter, but I'm almost sure that it is implemented digitally (it has several stages iirc) so won't protect the input itself from overload.
Have you run some tests just around your house or backyard? Try blowing gently on the mics - do they clip / distort?
If they do, does a bandana suit you? Lol! But it's a serious suggestion. Any kind of fabric over the mic would help with this. or those fur earmuffs that folks wear, but you'd look pretty crazy in these during the summer...
It's worth experimenting just to try to get to the root of the problem. Good luck!