You can run the stock mid-pipe with any of the cat-back systems.
The factory cats will absolutely dampen the loudness of whatever mufflers you install. An O/R mid-pipe will result in quite a loud system if you use straight thru mufflers like SLP or Borla.
Sound quality is a completely subjective attribute.
HiTech stageII cams, BBK Ceramic LongTubes, MAC ProChamber, Flowmaster50series, SteedaUDP, JLT CAI, MGW, SVT Focus Fuel Pump, H&R Race springs, Bilstein HD, MM CC Plates, MM FLSFC, Eibach Swaybars, MM LCA, MM Pan-hard, 3.91gears, AuburnPro diff, Moser31splines, 17x9 & 17x10.5 Bullitts, Dark smoked headlights w/ 55W HID, chin spoiler. 283rwhp/298torque (motor), 417rwhp/498torque (latest nitrous tune) email@example.com (motor w/ 1.77 60'), firstname.lastname@example.org (1.78 60')on nitrous.