Have the same problem myself. Washburn M-3SW. All solid wood. It's got a real nice, clean tone, good volume and sustain, but lacks the 'chunk'. You've done just about everything one can do. I did the same combo of mods w/a Cumberland ebony bridge and an Allen tailpiece. Also, Gotoh tuners from the Stew-Mac catalog. An intermediate mando is an intermediate mando. You've probably maxxed it out. Resign to having to pony up a couple of grand unless you find one at a yard sale or something. +1 for going to mandolincafe.com, also.

Will Parsons from Rock, WV builds very high quality, affordable mandos. I've seen several on sessions here in Nashville. Most were under $1500 and all sounded great.