We did download and read through the L6 Connectivity Guide V2.1o RevA - and that's what prompted us to ask about why we needed to use the PRE model as opposed to the full amp model. The L6 Connectivity Guide told us to use the PRE, but didn't say why.
I use a standard XLR mic cable for my L6Link connection, doesn't seem to give it any problems.
Regarding setting multiple DT's while using L6Link, the easiest way to test/program what needs to go on there, is using the HD500 edit software. You will notice all the various options for what can occur with routing. In general, it's also worth taking a look at how the fx blocks are positioned.
For example, a mono FX block prior to the amp block will sum the audio prior to hitting the amp portion. If you are using two amp models, there are specifics for how they occur, how they respond to panning in the mixer block portion, and also how the DT signal is being routed by the HD. You can set them up as stereo, as dual amp, and a variety of other settings - which are most clearly indicated in that edit software. This routing is also impacted by how the inputs are defined.
Regarding why you would choose a 'pre' instead of 'full' amp model, it's actually to do with the distinction of 'modelling' power amp response, vs. the Bogner portion of your DT's actually doing those power amp items.
In a nutshell:
-full amp models re-create the entire amplifier model, up to the cabinet. In studio/direct, the microphone and room sound is also modelled. In combo and stack poweramp modes, the microphone and room portion is excluded. HOWEVER, those output modes when used with 'full' amp models are still digitally modelling sag, bias, class A, A/B, pentode, triode, etc.
-When using the PRE versions of the amp models, the only portion which is digital is the preamp of each amp model - the tone stacks, levels, and drive/gain settings. The Bogner side of the DT then handles actually switching betwen various analog relay switches to emulate, in an actual analog / tube / power amp stage, what each of those amp models would behave like.
Here are some of the blurbs from the manuals, that are relevant:
Connecting Two or More DT Series Amplifiers
edited - removed incorrect info regarding L6Link using HD300/400, now just links to the connectivity guide.
Configuring the Audio Signal Fed to each DT Series Amp
As presented in the previous Quick Start steps, it is possible to configure L6 LINK audio signals and control/sync behaviors independently for up to 4 DT Series amps. This is all accomplished using the POD HD500/HD Pro SETUP - L6 LINK screens.
The SETUP - L6 LINK:AUDIO screen options to select your POD HD audio routings. These settings are all saved individually per POD HD Preset.
• Use the Multi-function Knobs 1 - 4 to choose the POD HD audio signal fed to each DT Series amp. Set the AMP 1 parameter for the first connected DT amp, and the additional AMP parameters for each consecutively connected DT amp. The available options for each DT amp are as follows.
• L, R or Left/Right sends the Left channel only, Right channel only or both the Left & Right channels (summed to mono), respectively. This signal is derived from the very end of the POD HD signal path, therefore, it includes all active FX and Amp Models. (Note that you can utilize the POD HD Mixer Block options to change what is panned to each of the Left and Right output.)
• Amp Model A, Amp Model B or Amp A/B sends the output directly from the respective Amp Model(s), wherever they reside within the signal flow. This audio signal includes FX Models positioned before the selected Amp Model, but not FX Models positioned after the Amp Model.
Note: that if your current Preset has only one Amp Block, then no “Amp B” actually exists. In this scenario, any of the AMP 1 through AMP 4 options in the above Setup screen set for “Amp Model B” will output the signal from the end of Path B to the respective DT Series amp.
Configuring the Control Options for Each DT Series Amp
The SETUP - L6 LINK:CONTROL options determine the “sync” behavior between POD HD500/HD Pro and each connected DT Series amp. When configuring L6 LINK Audio parameters for specialized purposes, for example, 4 DT amps all set to the same source for one huge mono backline, setting these Control parameters all to the same MIDI Channel provides the desired Control behavior. These settings are all saved individually per POD HD Preset, allowing you to create and instantly recall any number of different multi-amplifier configurations!
Use the Multi-function Knobs 1 - 4 to choose the POD HD Amp Model or MIDI Channel for up to four connected DT Series amplifiers.
• AMP A (CH 1): Sets Channel A of the respective DT amp to “sync” to the POD HD Amp Model A. (Also see “DT Series Amplifier - Channel A & B Operation” on page 3•8.)
• The DT amp will auto-configure its tube power amp Topology settings (Class AB/A, Voicing Mode, Pentode/Triode, and more) to match the current POD HD500 Preset’s Amp Model A.
• The DT amp Channel A and POD HD Amp Model A knob values (Drive, Bass, Mid, Treble, Presence & Volume) are synced.