playing more than 2 sounds with synth option

Hi!

I am playing 2 frequencies like this:
> play -qn synth $a_number_variable sine $sound_1 sine $sound_2 fade h
$some $random $numbers

and I am trying to play even more sounds like:
> play -qn synth $a_number_variable sine $sound_1 sine $sound_2 sine
$sound_3 sine $sound_4
or like:
> play -qn synth $a_number_variable sine $sound_1 sine $sound_2 synth
sine $sound_3 sine $sound_4

but that doesn't work. How would I do it to play 4 frequencies parallel
with the same command? Is there no support for that and if so, why limit
it to 2?

Thanks in advance for any help!

Noah