Some of the Belkin routers have hidden pages which contain information about your line and router.
For some reason they aren't linked to from the main web interface but you can access them by first logging into your router then using the following urls.

Line Stats (inc SNR stats)
http://192.168.2.1/ADSL_status_main.stm

Line Stats (error stats)
http://192.168.2.1/statsatm.html

Line Stats
http://192.168.2.1/adsl_status.stm

ADSL
http://192.168.2.1/adsl_para_main.stm

DDNS
http://192.168.2.1/ddns.stm

Firewall
http://192.168.2.1/firewall_spi_h.stm

NAT
http://192.168.2.1/nat_main.stm

QoS - Set up
http://192.168.2.1/qos_main.stm

QoS - Traffic Mapping
http://192.168.2.1/qos_clsmap.stm

QoS - Traffic Mapping Stats
http://192.168.2.1/qos_stats.stm

WAN
http://192.168.2.1/atmint.stm/3
http://192.168.2.1/isp.stm

Wireless
http://192.168.2.1/wireless_e.stm
http://192.168.2.1/wireless_wep.stm
http://192.168.2.1/wireless_wpa.stm
http://192.168.2.1/wireless_1X.stm

CLI

It would appear that these routers also have a similar chipset to the USR 9106 router, in which case commands such as "adsl info --stats" will work if you ssh into the shell.

There is more information about the busybox shell commands on my Voyager 2100 CLI page which also has a similar chipset.

You can access the CLI using AxeSSH (Shareware - download here).
Increase the screen buffer lines to make sure any long responses don't vanish from the buffer before you can copy them - set to 1000 lines to be safe.

amci on adslguide writes

I've found that the value you should use for the "ADSL configure --snr value" command should be the percentage of your default margin as set by BT - so if your default is 6 for example, and you want to force it up to about 9, use ADSL CONFIGURE --SNR 150 (9 being 150% of 6), or to force it down to about 4.8, use ADSL CONFIGURE --SNR 80 (4.8 being 80% of 6). Be aware though that snr varies continuously though, so the percentage applied will be of the actual snr at that millisecond, which is why I say you can set it to "about" 4.8 for example.

Theres some more useful information about the belkin router in that thread which may be well worth a read.

Its worth pointing out that "adsl info --stats" has a bug which means the line uptime never shows over one day, but the correct uptime since the last router resync can be obtained from "sysinfo".

Thanks to rhenn for bringing the CLI information to my attention.