Across:
   8. Second and fifteenth outing of 3 not the main event (8)
   9. Firm, taking time (6)
  10. Dio tour as regularly as late singer's former band (5)
  11. Sleep a while, in the bear's fashion (9)
  13. During Deep Purple number, Sullivan comes out for a vocal (8)
  15. Mush rife at sea, requiring removal of regular bits of fish bones (6)
  17. Keep a lid on wild action around north (7)
  18. Mujahideen leader gets around to organisation of terror, forming two new cells (7)
  20. Spread out, density primarily being small (6)
  21. Great wagon of sorghum, a hay an appaloosa consumes (8)
  22. How Democrats want folks to vote this year: keeping dreadful leader not an option! (9)
  24. Instrument 25 almost turned into heavy metal? (5)
  27. Mush rife at sea, requiring removal of regular bits of fish bones (6)
  28. Using cunning in crafty extremes, always split 50-50 (8)
Down:
   1. Milo prepared as treat for young stars (4)
   2. see 26
   3. Band after the wild hot ones originally (3)
   4. Where you see shops advertising new beginnings start out (7)
   5. Amazing gift is whole big festival venue (4 2 5)
   6,23. Playing a banjo? Easy for commercial musician! (4 4)
   7. Wrong to replace swearing in debate, as it changes the tone (10)
  12. I'd jinx her; I'm terrible as a lead performer (4 7)
  14. Element of sulfur in Vietnamese dishes mostly rust (10)
  16. Muse? Bloody tricky band! (5 5)
  19. What Democrats wanted the house to do with him not bearing initial fruit (7)
  23. see 6
  25. Essentially unpollutedly retro rock'n'roll band, in short (4)
  26,2. Wild teen, Ray on surer ground when taking the lead in a rock band (3 5 5)