There was a warning on one of those links
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WARNING! Never plug
powered outputs that are designed to power speakers (like those from a power amp or a powered mixer) into your soundcard. Doing so can cause serious damage at best and a fire at worst. I know someone on another forum who plugged a 150watt amp into his soundcard and it caused a fire, melted the cables, and took out both his computer AND amp. So please be careful when dealing with this type of equipment!
Connections from non-powered mixers, direct ouputs, aux outputs, headphone outputs, effects units, and even direct guitars/basses are perfectly safe to be plugged into your soundcard.
If you are unsure of a particular connection, it is always better to be safe than sorry. So please ask before connecting it to your soundcard.
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My amp has a line out and I'm wondering if it will be ok to connect to my soundcard. My amp fits in the powered output which is a no-no to connect, but it has a line out which seems to fit in the ok-to-connect category.
What should I do?