I upgraded my Zoom H1 to a Tascam DR-40 and preliminary tests have me very happy. I did run into an issue trying to get my new Audio Technica wireless lav system working with it, but after a few hours, I figured out the problem.
Neither the receiver, nor the transmitter for the Pro 88W have a volume control or any form of level control. And the receiver puts out a VERY powerful signal that was overwhelming the DR-40. I had the levels on the DR-40 all the way down to +1 from +100 max and I was still getting peaks.
I got frustrated and went for a drive (I got a 40% off coupon from Harbor Freight that expires today). When I got back, I started organizing all of my doodads into a new toolbox I bought and ran across this radio shack volume control I bought last year and never used:
I stuck it between the receiver and the DR-40 and BINGO! That fixed my problem. The audio sounds fantastic and I can bump up the levels to the 50s and still keep it under -12db.
DSLR Film Noob and CheesyCam are pitching this which will also probably work: