I have not heard of the terms AHD-L, AHD-M, and AHD-H. From speaking with Nextchip, they describe their offerings as 960H (legacy SD+), AHD1.0 (720p) and AHD2.0 (1080p). I think your terms match with those. Assuming so, AHD-L / 960H, is an NTSC / PAL signal so it should integrate with any traditional matrix switch and display as a conventional 4:3 SD analog feed.
Since the true HD analog formats use a different format / signaling, I do not think they will work with traditional analog matrix. That said, I am going to ask Pelco for comment and will report back.
Even if the Matrix supported the signal, the matrix outputs would need to go a HD Analog Monitor.
I agree with John that an old-school Pelco Matrix Mixer won't work. It might pass some signal but not much. Because the best specs I see are capable of passing no more than a 15Mhz signal. The Analog variants, AFAIK, require around 75Mhz.
On the other hand, unlike magical format converters who must account for specific high-level protocol differences, a switcher with the right electrical characteristics should be able to accommodate all analog CCTV formats, including NTSC, PAL, 960H, 1280H, AHD, CVI, TVI, without sleight of hand.
Aliexpress shows a couple of early attempts at just such a switching matrix, here's one touted as 120 Mhz capable and CVI/AHD/CVBS compatible:
Also, I'm not convinced that HD Analog Monitors are the only possible destinations. One might dup a stream for recording, or perhaps have one be placed in front of a HD encoder driving HDMI monitors.
In the good old days multiplexers were installed and controlled by the matrix. With the cost of HD DVR's I could see one at each monitor. 16 outputs could be mapped to the DVR and then the Camera View (1/4/8/9/16) could be managed by the switch using serial or network control to the DVR like they did with the MUX. Decode/Local Record. Just a thought. Old Matrix could have new life with updated boards. The HD DVR's accept SD and HD.