Resistor for headphone output on guitaramp?

ForHerDeadEyes

Señor Member
Jan 24, 2011
901
32
28
Sweden
So have a couple of amps that I've removed the speaker from..
I've been using the headphone outputs with my PC..

The specs:

Peavey Rage 158
Headphone Output:
Load Impedance: 4 ohms
or greater
Nominal Power Output: 20 mW into
4 ohms
(Stereo jack, monaural signal,
disconnects internal speaker when
phone plug is inserted)

Crate GX-15:
Output Power Rating 12 watts RMS @ 5% THD 4 ohms, 120 VAC
Internal Speaker 8” Crate Custom Design 4 ohm
(Doesn't say anything about the HP output)

The Crate works without any issues, but the Peavey almost sort of electrified my equipment..
A few resistors in between the HP and PC/DI-box solved the problem, but it was a pretty crappy temporary solution..

I'm wondering if I can just use a single resistor?
I thought about making a loadbox with a single resistor (50W 10 ohm) and making it line-out..
But I guess just using the HP output works fine.. (complicated to make a loadbox with line out?)
But with those specs for the amps in mind, (even though the Crate works fine, I'd like to be safe) would it work to just use a 10 ohm 0.25W resistor or should I use several/and or just a single stronger than that? or weaker? ex. 5W 4.7 ohm or a 1W 4.7 ohm..

I can't grasp the effect a resistor has on the audiosignal (Watt & Ohm), I just don't want to fry my gear.. :D

I asked about building a loadbox on the stickied thread about DIY loadbox etc.. but.. that thread was removed, so I never got an answer..
Hope I'm not asking anything that's against the rules (since the thread was removed)..
Thanks!