Single output driving 3 others with a 1 to 3 adapter or two Y's in series could cook the audio amplifier of the sound card. Additionally audio quality will likely be horrible as the wave forms amplitude is getting crushed by trying to drive into three amplifier inputs so it wont sound as clear and possibly muffled some.
I've done a Y with headset and loopback when mixing music for fun to hear it as I am play/recording where I send the output back to the input of the same sound card. Never connected more than 2 on a single output like that.
A better setup would be to have an amp that connects to the PC through a single connection that has auxiliary outputs from that amplifier to drive other devices as a team of speakers etc. I have connected a PC output to auxiliary input of a stereo for example that supported surround sound and that was safe from cooking a PC Sound card.
