Q: Does the Apogee ONE XLR Input accept Line level sources?

Yes, your ONE will accept the output from your guitar amp. Make sure to set your level properly as to not clip the signal.

I have almost the same question…

My guitar amp has a line/headphone level output with a jack (TRS): can this output work with the jack input of the ONE?

Can this input stand the level of line/headphone from the amp (Blackstar HT-5)?

MFC,

ONE's 1/4inch input is TS or guitar cable unbalanced input. You can use a 1/4inch to XLR cable to connect the output of your Amp to the balanced input of ONE through the XLR connector.

Hope this helps!