I am planning to buy a Ketron SD2, and need to understand how it is going to be connected to my PC.
I've searched the subject already but I am still not sure on a few things.

I use a TASCAM US-144MKii (it has MIDI OUT AND IN jack which are currently not being used).

I have connected my speakers to the Headphone output on the TASCAM.
(In the BIAB Midi/Audio Settings, I have Midi Input to TASCAM, Midi Output to TASCAM... and so far I use the Roland VSC DXi, and in the Audio Driver Setting, I have the TASCAM seleced for speakers in the AUDIO out window.)

Occasionally I need to use my Behringer Mixer so I prefer that it stays OFF but connected to the TASCAM just in case (Stereo RCA cables from Mixer's Alt 3-4 Channnel to TASCAM's Stereo RCA Input, and RCA cables back from TASCAM's RCA Output to one of the Mixer empty stereo tracks).

I see the SD2 has MIDI IN and THRU plus STEREO RCA Out...

If I had to guess, I would connect the MIDI out from TASCAM to MIDI IN on the SD2. Right?
Would I also need to hook up the RCA out on the SD2 to TASCAM's Input Channel (where the Mixer is currently plugged in)? and Why? I've never use a midi synth so far, so I am not sure...

Would the SD2 show up as one of the choices in the BIAB Midi Input/Output menu window, or just the TASCAM?

If I decide to keep the mixer plugged in, Can I plug in the SD2 to the Mixer, using RCA cables from SD2's Out to one of the Mixer's free stereo channels? And would I still be able to see the SD2 from BIAB?

My uses for the SD2 would be 1) to improve the quality of sound coming from BIAB as back track while I play my guitar, and 2) record my guitar along with music made in BIAB (in BIAB or RealBand). I am not sure it that is the same when rendering my music to CD or mp3?

Thanks in advance.

2008 Gibson ES-339 Custom & 2010 Les Paul Traditional. Fender SCXD Amp
BIAB/RB 2015 UltraPAK + Ketron SD2
Windows 7/64 Intel i5 3550 PC, Tascam USB144MKII
Behringer X1204 Mixer
Bose Companion 3 and/or L1 II w/T1 + SM58 MIC