Hi, and welcome!!
I'm not too up-on the LSS amps, but I can answer this....
(let me set this story up): I play with a Road King combo in my band, and we play pretty loud. We're actually in the middle of a 2 week stint at the same club and we had practice last night at the club. I don't like leaving my Road King at the clubs over-night, so I take it home every night. I didn't plan on cranking up too loud last night, so I just took my 30+ year old Fender Deluxe 22wt amp and my Vox Tonelab SE to practice......Well, our practice turned in to a "Paid practice" since there is a restaraunt in the same building as the club and everyone started wanting to hear the band. We ended up playing for about an hour and a half doing our "Best of" set list at full gig level and I was using my little 22wt Fender amp mic'd up thourhg the PA and it sounded GREAT!! I definately missed my RK, but I was impressed with my Deluxe's performance and now know I have a decent backup if my RK ever goes out (or when it goes in for the diode update later this week).
Not sure of the wattage on the LSS, isn't it 30wts?? That should get you by just fine, unless your used to a super loud stage volume.
Good luck with the gig, and have fun with your new toy!! Let us know how it went :wink:
EDIT: I did forget to mention that an extension cabinet will push more air, which will, in-turn, give you more volume and more head room on stage. But I guess what I was getting to is that the amp by itself should handle the gig with no problems.