As with most other interfaces (and here's the actual quote from Scarlett 2i2 Manual):
"Scarlett 2i2 has no “Mic/line” switch – the Focusrite preamplifier stage is automatically configured for a microphone when you plug an XLR into the input, and for a line or instrument when you connect a jack plug."
So, to dumb it down - plug the bass into GAP, then spread the cable from GAP to Scarlett (on GAP it doesn't matter whether you use XLR or TRS jack, but the end that goes to Scarlett MUST be a TRS jack), and that's about it, this way preamp on the Scarlett won't be engaged.
I don't watch porn... I have MTV for that.
Instruments: Sonor Force 2007 drums, Pearl MCX snare, Paiste and Zildjian cymbals, Peavey 6505 amp head, Custom made 2x12 guitar cabinet, Maxon OD-820 pedal, Ddrum triggers, Alesis Trigger i/O,
Recording/Mixing: Shure SM57, Audio Technica AT4041 x2, AKG D112, AKG C430 x2, AKG D40 x3, Rode NT1A x2, Audix i5, Thomann SC1100, Thomann SCT800, Focusrite Saffire Pro 40, Behringer ADA8000, Yamaha HS80M x2, Radial Pro RMP, AKG K171 MkII