So I guess that would apply to running 4 speakers off a small amp.

No, a small amp and a head unit are two different things. Most "small amps"
are 2 ohm stable so you can do it with no problems. And if you're talking
tweeters, then you could do it on a head unit with no problems either.

I
have a 88 watt 2 chann amp driving a pair off 3 1/2 door speakers. I
want to add a pair of 1' tweeters on the dash.

Why?