Are you trying to skip the pesky 3 capacitors, two resistors just after pin 18, "VoiceOut"?
Bad idea.
But, as explained in the link given, if you want to use a simple "speaker" (WITH AMP) system meant for a PC, then you should be fine if you connect that.
The imformation that you gave about your amp+speakers passing the "hum test" was encouraging.
Just replace everything to the right of the 10 uF cap (previous post) with your speakers+amp.
Be sure to connect the "other" side of speakers+amp to Arduino ground. Be sure any electrolytic caps are plugged in the right way around.
Try to solve this before the 24th, and post what you found to be the problem here, so we know what newbie gotcha to warn others about the next time. (After the 23rd, this forum is being frozen....