His problem is he's using the 3DS format.
3DS is a "triangles only" format. (No matter what the source app says the faces are, quad, n-gons, whatever, as soon as you export as 3DS, it's all tri's.
3DS does not support any other type of geometry.
Use OBJ and it will maintain the quads.
You'll have much better results and much less cleanup.
You can use Wings3D's "Untriangulate" command which will convert the vast majority of the tri's to quads.
You can then use Wings to straighten out the rest, keeping the mesh as much quad-based as possible, and using "Turn Edge" to make sure the edge loops flow correctly... good edge loops in Wings will transfer very nicely into A:M as closed splines.
Keep poles to a minimum (vertices w/ < or > 4 edges attached) as A:M will have a hard time figuring out the proper spline flow through "poles".
Also, you may note, due to the inherent differences between Hash splines and sub-d polies, that polygonal meshes will "bloat" a bit, caused some face intersections, and the model looking a bit "fatter" than the original poly-based mesh. In Wings, you can select the entire mesh in vertex mode, and a apply the "Tighten" function at ~ 78% before exporting as OBJ and the mesh will be close the the correct proportions when imported into A:M.
If your careful, you can prep a poly-based mesh in Wings for import into A:M with minimal cleanup and not even lose your UV mapping.
hehe... a member since '03 and I'm still a "Newbie". Actually bought A:M at v5 when it was still "MH3D".
If anyone is wondering, "What's "Wings3D?", it is a poly-based modeling app that is FREE.
Available at http://www.wings3d.com
It can come in handy when trying to get poly-based meshes into A:M.
Back in the A:M v6/7/8 days, it actually had a A:M MDL exporter written by Howard Trickey... a name that is pro'lly familiar to some of you A:M "ol' timers."