look on the back of the system where the speakers connect. it will hopefully say 4-8ohms. If so your fine.
a small number came with there speakers and were never designed to do anything else. adding more then becomes an issue.
from your amps point of view, it could be happy pushing 10 watts through a speaker of 8 ohm resistance(impedance) but if you give it two speakers of 8 ohm then it will try and put 10watt through each. This is why adding more speakers causes strain on the amp. There are two ways of wiring the speakers though. parallel or series. parallel ive described, it gives two routes of 8ohm for the amp to put power down. series would be daisychaining the speakers so the amp has to put power through one speaker, then the other before back to the amp. in a row. Pushing through one, then another is twice as hard and means you now only get 5 watt from the 10w amp. This wont warm it up any more than usual. less infact.
Valve amp users should ignore this post.
tbh it sounds like a midi system. do whatever you want with it its no loss lol. If it distaughts or runs hot im sure you will turn it down. Just dont let kids near it as we all know that only volume level 10 exists in there minds