What are feet like? Companies that make trail runners, like those that make boots use a variety of different lasts. What are your Asolo's, high or low volume? Straight or curved last? Do you use orthotics or not? Do you want to use a thick sock or thin, or a thin liner with a thicker second sock? All of these affect fit.
And then how stiff do you want the shoe to be? Several Montrails have a full length plastic plate. This makes them generally stiff (though less so than most boots) but offers benefits similar to a full length shank in terms of lateral stability and protects the foot from feeling the rocks. Their newer models, Sabino Trail and AT tend to run wider than most, and pretty much true to length. The AT so far seem solid enough for off trail hiking/backpacking.
Asics tend to run true to width and length and without the full length plate are much more flexible, and lighter. I find them good for good trails, but a bit to soft for rougher trails, and would never consider them off trail.
New Balance (the only other trail runner I've tried) tend to run a bit short, but have the most options as far and both size and width are concerned. I couldn't get a good fit in them when I started wearing orthotics.
My favorite trail running shoe ever was the Montrail Continental Divide (no longer made). Not as wide as the new Montrails but with the full length plate.
In any event, the key is finding the right fit. I suggest finding a running shoe shop or shoe store that will do a custom fit assessment and then recommend shoes based on your foot size and shape. If they don't carry what you want, use that info to order several different models from several different companies from Zappos or other online store. Zappos and many others have user reviews on "true to length" and "true to width" that can serve as some guidance.
I've had as many as 12 pair (5 models, 2 lengths, and in some 2 widths) arrive at once. I wear each around the house for a couple days and narrow it to a couple keepers then send the rest back. That is how I found the Continental Divides, and how I found the Asics Trabuco shoes, both of which served me well.