Here is another thread.

Every guitar player connecting to Backtrack with his guitar directly, suffers the same dilema.

The recording volume is way too low. Since ever semi-professional guitar player likes to record dry guitar to add effects later, will record dry to backtrack. Every guitar player doing so, will suffer the problem that Backtrack recording volume is much too steardy, it should be much more  sensitive to lower volumes.

There fore please Line 6 programmers, add a option beyond 'soft' recording volume in Backtrack setup utility.

Ps. Myself I have to pluck my strat strings pretty hard to even initiate the Backtrack recording feature, must hit very hard to keep it recording