Hey Austin, since some of the more knowledgeable guys here haven't piped in here yet , I'll give you my 2 pennies.
You didnt give us much to go on. Not sure which Line 6 you have so don't know how many watts or what size speaker you have,or if there is line out or an out jack for an extension speaker? I know most of the Line 6 amps have effects built in so assume you are not using any pedals other than the looper? I'm not familar with the Line ^ circuitry or if turning up the treble and midrange would help you cut through much like it will on a fender.
The simplest way to get a few more decibels out of your current amp is an EQ pedal or a boost(think overdrive pedal). The MXR 10 band EQ claims to boost the signal 12 decibels though I wouldn't necessarily recommend that pedal. I saw a Boss DS-1 for sale on the steel guitar forum for $25 . My Ibanez TS-9 tubescreamer really boosted the signal. Along with boosting the signal they will change your tone though. I'd say that would be the most bang for the buck. But really,in the long run would think about upgrading to a fender(or many of its clones) tube amp if you want the tone. Like a Deluxe, Princeton, Deville or even a Blues Junior will get plenty loud if you don't need to stay clean.If you really want to get loud and clean there are getting to be a lot more of the Reissue Twins around.I wouldn't pay more or even as much for a reissue just because they are newer though.The really good deals on the silver face twins are becoming fewer and farther between. Set aside a few hundred bucks and keep your eyes open for a deal.
Manifest. Musicians in distress are frequently unloading their used gear for cheap.