Here's how I set up my 'rig' perhaps an alternative to the four wire thing,..a variation on the typical wet/dry rig.
This is great for small watt tube amps with no fx send return or line out or channel switching/boost.
Traynor darkhourse or Vox AC4c1 routed to groove tubes SE11 attenuator/speaker emulator[lots of routing options here]
Using 'return' of groove tubes fx loop to guitar imput of HD 300, line out of HD 300 to a nice clean[prefferably S.S. amp with line out and either built in speaker or cab ] -in my case an old Acoustasonic jr.[no line out] -Insert frowny face here.
I use only the FX of the HD, and the organic output tube saturation of the tube amp, and use the volume pedal to blend these sounds up and down in and out so's there's no real need to stomp an FX on or off, usually...
I see no need for an a/b/y box, and no 'click' or 'pause' of one.
Heavenly sterio effect, and way for 'hi-fi' than any FX between pre and output stages of the 'typical' tube amp with FX loop employed, as any tubes fx hit will be washed somewhat.
[it's how the REAL studios do it {usually post production thou} and you can have that at home!]
I got about $1500. invested with three amps mentioned, Se11, HD300 et al.
Add a mike push record and capture real speakers thru real tubes in a real room, like God intended. And without the cops coming.
Great sound for studio and reheasal. Live maybe a powered monitor with a small mixer the sound guy can't get his hands on [Also this would eliminate the need for the Groove tubes Se11, but you won't be able to duck down on the speaker without it or some attenuator with a line out.]
Also, if you play mostly clean set the amp for that not the L6, and use l6 amp models for ocassional dirt, and for mostly dirty like me I'd use the amp model of L6 for the clean tone.[Fender baby]
For me, i just need the L6 for quik acccess to FX, wah, volume and tuner, really.