Mods play backups period. -r/+r doesn't matter.
I would get a Messiah 2 over the Magic 3.1. It is more reliable and doesn't have booting problems.
Your v5/v6 should be able to play both -r and +r.
Being able to burn at 2.4x over 2x is really the only advantage +r has over -r. Their 1x and 4x speeds are the same though. The downside to +r is that media costs more.
I believe the Sony is the only burner that does both -r and +r. I personlly like -r media as it is cheaper than +r.
US V7 PS2 w/ Apple Pro
LG GCC-4480B 48X24X48X16 CD-RW/DVD-ROM Combo