[janoskiss (Steve H)]

A barlow's good to have no matter what EPs you have. Your nice 15mm Parkes Gold in a good barlow will serve you well for what you're after at the high power end. I'm not a powermate fan (yes, they do work well with no ER issues for long FL EPs, but can't beat a well made 2-element barlow for mid-high power IME). I had many EPs and barlows (and a P'mate) and the EPs come and go but I will always keep my two fave barlows. You can also use inexpensive extension tubes with a barlow to give you a lot of flexibility in magnification.

EP recommendations for your scope: Pentax XF 8.5mm & 12mm - gorgeous EPs and a perfect match for 8" f/6. (I wish I so wish I still had mine!) - and if you combine these with a good 2x barlow you'll have the best of deep sky, planets, and anything else the distant cosmos can throw at you covered.