Using a Mesa card input to monitor EMI emissions with Halscope

I learned I could measure EMI in my system by using a floating wire ran along the wire races containing my control and logic signals. I get the e-field noise connecting my probes ground to the panel and probe to the end of the wire and b-field by grounding the other end of the floating wire in the same probe configuration. I would like to connect a physical probe to a mesa card input but im not sure yet on how to go about it. 

I would need a input that could read voltage and i would assume i would need to wire a BNC connector to that input I have a 7i96 and 7i84 is there an input suitable? I dont know enough about what Im trying to do to actually pull it off. But when i started doing this cnc project few years ago I was in the same any input would be helpful. I think having a way to see and track emi over time would be helpful troubleshooting the tinkering and upgrading i seem to do i could see if emi is affecting performance in a measurable way. it would be cool to add a tab to my gui with those halscope screens so i could take a look at a glance theres just a lot to this idea im still unpacking and brainstorming 

A scope is cheaper than any Mesa card, the MiniWare DSO211 is ~40$ and 212 is ~60$ for two channels.
To "safely" use the Mesa field inputs, 7i84 set in Mode 2 should have 4 analog inputs (00-03) at low resolution and low speed, add a resistor to each input. Probably will not be enough for what you need.
Using FPGA inputs as logic analyzer with some resistors is OK, but care must be practiced as those inputs are very sensitive, and adding zener diodes to each input is advisable. These inputs are fast enough for most uses, are 5V tolerant but with 0-3.3V range.
Any of those will not be very usable for finding interference as all above are DC coupled, whereas you would need AC coupling to measure interference.
And to make things worse, interference from cheap switching power supplies and motor drives and VFD's can in some cases be over 60VPP (volts peak to peak), meaning it can easily destroy any of the above setups.