These are all line level. The T1 only allows mic level, XLR balanced inputs correct?
The T1® can most likely accept the line-level XLR inputs from your Guitar preamps and your Bass preamp.
Any plans to make the XLR inputs on channels 1-3 line/mic level switchable?
I believe that the T1® XLR inputs on channels 1-3 were designed to accept inputs from microphones up to normal line-level inputs without needing a switch or a pad. This is in unlike the Model I (or Classic) Power Stand where a pad
is recommended for line-level inputs.
If you have the XLR-XLR cables, Please give it a try and let us know if you have any issues.
edit: link to pad