you can try your luck by loading rockbox and EQ with line out on your 5th gen.
I just got myself a Ipod 5.5gen and loaded rockbox. haven't tried out much on the EQ yet. will work on it this weekend to see if I can get some improvement.
I also have the 6gen ipod, and although the line out seems slightly clearer and soundstage and seperation wider, I think I prefer the slightly warmer sound of the 5.5gen, with slightly tamed highs.
but yeah, the TTVJ is really nice and I also get that certain sweetness after some time. actually sometimes I feel the sound gets really nice after an hour or two, ..not sure why that is, or whether its just placebo, but I sometimes feel there is more harmonic distortion...
as for better source, that is a difficult one. I also thought about the solo but realistically it becomes a brick and unless you use your setup transportable a lot, its a lot of $$..there are better DAPs coming out now slowly so I expect better sources for all of us in the near future.
There's always the imod/whipmod option but thats also a lot $$...unless you can DIYmod and then increase your 5gen to 240gb. otherwise with the new DAPs (cowon D3 & fioo X3 with both dedicated digitial out) thats coming out not sure it is worth the money spent. I suspect we will see more and more imods for sale as better DAPs come out. I think the use of imod has passed its time and coming to an end in its sound advantage compared to others. of course they still sound nice and will hold their own in sound, but will lose out in functionality, battery, size etc. though they are king in size once you bump it up to 240gb. and the reason why I got the 5th gen, I really like loading up all my music as I do travel frequently and like going away on weekends etc.
EDIT***
for the ping, I don't get it unless I bump it. so shaking and walking with it I have no problem. the only real downside to this amp is its opposite inputs. if I tap the LOD (hard enough), I do hear a ping sound, so carrying it needs some ingenuity to com e up with a good solution. so I would count that as its only downside. otherwise, the size is pretty good, matching ipod, iphone etc. thickness is also good. build is very good as well, and though doesnt look very flashy compared some other amps out there I actually like its spartan, industrial look.