I must admit that at the beginning I experienced the same thing: "muffled" and undefined sound. Here some tips:
- The standard presets are bad. Do no judge the PODxt+BP on the bass presets and do yourself a favour: delete them.
- When you change amp/preamp the PODxt changes automatically: pre-EQ, cabinet, mic, mic-distance. I wonder why especialy considering that the person that designed these automatic settings may not have the same taste that everybody else. This "system feature" makes the editing very difficult indeed. However, there is a solution. I use Line6 Edit. On the right side of the amp type selection, there is a small chain. If you click on the chain, you disable the automatic settings. This makes the editing much simpler. In practice I believe there is a way to define the automatic settings associated to every pre but to be honest I prefer to have full control of the unit.
- The knobs are very sensitive. I suggest to start any editing with the EQ knobs on 12 oclock (however, I think, some models have the linear position on 0). No compressor, gate or effects. Then turn the EQ knobs by small amounts and only one at the time.
- I suggest to start with just preamp and no cab modelling. I get better sounds in this way. You can always add cabs at a later stage.
- The line6 documentation is not well written. Overall it is not bad but sometime I need to move back and forward between BOD, POD and model pack manuals. Other things like how the POD knobs map to the model packs are simply not written anywhere.
- The parametic EQ is a nice feature but personaly I almost never use it. Once you mastered the amp models and the standard EQ, the parametric EQ is almost pointless.
- The DI xover frequency default is 400Hz (why on the model pack? Who knows...). This makes any effect sound horrible (IMO). Set it to 0.
I hope the above helps.