I have the equipment that you discribe above (flextone 3 + HD500) And is an awesome combination!
1. Best Seting is to use full model of the HD, with the 4cm, and connect the flextone to your computer (via midi) use the line 6 edit on flextone and set it to tuner.That way you will use the speakers of the amp as speakers without any simulation of power amp, same like a FRFR,
2. Not any downsides.
3. It is awesome aproach, worthy, and onether thing you can do is to use the 4cm, pre or full model on the HD, and a model on your flextone!You can discover some great new tones you never imagine!
P.s. Try the full amp plexi 45 from your pod with the ac15 of you flextone. You will remember me
Before line6 was called line6... they used to do r&d for other companies like alesis + others. and when those customers came to visit the offices of line6 (before it was called line6) and the receptionist needed to warn all the guys who were designing products for other companies (and for themselves... ) who were like 'in the back' the receptionist would announce over a tannoy 'tellephone call for 'fred smith' on line 6' the cunning part was that they only had 5 telephone lines, so it was the secret code for "hide your sh1t the feds are comin'" or "someone's coming, let's hide these PODs that we aren't going to release for another few years so they don't see them"
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