Just so happens I solved the hum issue with my Laney Ironheart today and was browsing this forum for the first time in ages. So this coincidences allow me to reply to your question about solving hum from the Laney amp - assuming it is ground loop hum.
I've been having this problem with the Laney for ages and never quite managed to solve it. Quite a while ago I bought a Behringer HD400 passive hum destroyer (very inexpensive) but never got it to work. I realise now I was using it wrong - trying to connect both the send and return of my amp to it. Here's what I did today. I just connected the HD400 to the line that was going from the POD HD to the amp's FX return (so just using one input and output on the HD400). Thus breaking the physical connection (but not signal connection) between the pre-amp and power amp. And the hum was gone. Can't believe it's taken so long to do this.
And thus I've been enjoying an almost silent 4CM with my POD HD500 and Ironheart this evening. Tonight I even experimented with the 4CM method that doesn't use the POD's FX loop at all. Guitar > Pod Guitar Input > POD Signal path B > Guitar amp input > Amp FX send > POD Aux Input > POD Signal Path A > Amp FX Return. Can't believe I've never tried it before, works a treat. The only downside is you can't use the looper.
Interesting discussion on routing this. It took me a long time to figure out the signal routing on the HD500 myself and I bought one the week of release. It was finally realising that both the A and B paths were separate stereo that made everything fall into place. I tend to build patches totally in one signal path now - it's my preferred method. I keep A and B completely separate. I almost never put pre-effects before the split, always fully in the side paths before the amp, then after the amp.