Cichlid vs. Cichlid

Hi,

I'm having problems with a pair of butterfly cichlids (I think- aka
purple rams?) which I recently introduced to my little fishtank (11
gal).

The tank started out with one plec (who unfortunately we had to use
for cycling since he was rescued from another tank before this one
could be cycled any other way), then after cycling we added three male
guppies. The guppies are fairly antagonistic towards each other and
we're on the lookout for a female to keep them company - apparently
this will calm them down? They don't seem to do too much damage to
each other though.

Recently we added the two cichlids. We were advised to get a pair, and
that they would be fine in the tank with the guppies. Indeed they
don't pay any attention to the guppies whatsoever and for the first
week got along fine together.

Since then the male has done nothing but chase the female, and she's
beginning to show the scars of unwanted attention - a rather nibbled
tailfin. As far as we can make out, the reason for the problem is that
if the female doesn't respond to the male's attentions, but does
remain in his 'territory' he will start attacking her as an intruder.

Is there any way to sort the tank out without getting rid of any of
the fish we have? Some of what I've read suggests we should put more
fish in, to break up territories and give the male ram something else
to think about. Won't this lead to even more fighting? And if it is a
good idea, what sort of fish do we get- more cichlids? Or just fish of
equivalent size?

Thanks,

David