For a while there I thought I'd have to change my amp as it doesn't have the usual send and return sockets for effects at the back, just the one instead. I had assumed that I'd need to connect to the back of the amp as if I went through the front, the preamp would colour the sound too much, however, I spoke to a guy yesterday who said that he regularly deals with Marshall amps direct and the advice that comes from their designers is to never use any kind of distortion effect through the effects loop; they must always go front end. Initially I wasn't too happy about this because all of the advice I've had so far tells me that if I go through the front end the preamp will colour the sound too much and destroy the effect I'm after, which is essentially overdriven to high gain valve amps at bedroom sound levels. He was now telling me that I couldn't go through the back either as the distortion destroys the connection! I don't see why that should be but he said he was just passing on what the designers of the amps had told him. He told me that he'd been playing for years and tried loads of gear and as long as I was going through the clean channel with all controls set to 12 O' clock then any colouring of the tone would be negligable to all but the most obsessive about their tone.
I wouldn't have thought that using a Pod XT Live through any solid state amp would colour the sound too much, though I can see how going through the front of a valve amp might. If this information is accurate, and I don't see why it shouldn't be, then I might as well get one of the multi FX units, run it through the front of my existing amp and then leave changing the amp until the end of its natural life and then maybe change it for a PA style system.
I will certainly try them side by side and I do intend to take my guitar and amp there on the day. I think it will boil down to where my priorities lie. I'm not really a huge effects junkie so a million different effects in a unit doesn't bother me, though a little chorus and delay etc. are nice - the usual suspects in fact. My main priority is to get a decent range of valve amp sounds at sensible bedroom levels as I fiddle around with things between BB King and Synyster Gates, though I mostly prefer the gain pushed up a bit. If the multi FX unit can give a good simulation of a high gain Dual Rectifier then I'm a good part of the way to where I want to be. If I had the room or played in a band then I'd simply get a good valve amp, shove a good distortion unit in front of it and maybe invest in a couple of decent stompboxes. Sadly I'm not in that position so I need an alternative and these modellers seem to offer an all in one solution that would suit my current situation but also be able to grow with me as my ability improves and possibly other opportunities present themselves.
I'm not sure if that clarification helps at all :D