I own the Tascam DR-60d and have really appreciated its user-friendly, rock-solid performance. I have used it in many different configurations and never had any problems or noise issues. You can get a used one for under $150 and get some quality used mics/accessories (stand, clips, bar, cables, etc.) with the remainder of your budget. I have made many matrix recordings in smaller venues using AKG 461's (used $500) and/or Studio Projects C4's (new $350 with multiple caps) into channel 1/2 with phantom 48v and sbd (line-in) into the 3.5mm mini input (channel 3/4). There are plenty of internal gain settings and easy and relatively quiet external gain dials. I have also used channel 3/4 mini to directly power my CA-14's through PIP while powering my AKG's with phantom (though you can use UBB). The BE thing is that you can run this entire rig with a simple and cheap 5V USB battery pack. I have a 20,000mAh usb pack that cost $20 and runs my rig for approx 15 hours. Can't beat that! There are tons of examples of the 60-d in the Live Music Archive to listen to.
Also, you can still run 4 mics with it and use your M-10 for a soundboard feed if available. Personally, I don't think an external preamp is necessary these days since the recorder pre's are good quality for loud music (unless you want the coloration). Besides, its just another cog in the system to account for (and another thing in the bag). Good Luck