For what it's worth, I found a solution. I can read measurements from the DM3058E over USB using Python.
Here's how I did it on Windows 10:
1 - Install the NI Visa runtime (It's free. I used the version here:
http://www.ni.com/download/ni-visa-run-time-engine-15.0/5379/en/)
2 - Install Python if you don't already have it. I used Python 3.4, x64. (That's free too.)
3 - Install the PyVisa module (home page is
https://pyvisa.readthedocs.io/en/stable/index.html). All you have to do is this:
c:\Users\Dave> python -m pip install -U pyvisa
Python will download the package and install it by itself.
4 - Now start Python and you can do this:
import visa
rm = visa.ResourceManager()
print(rm.list_resources())
That prints:
('USB0::0x1AB1::0x09C4::DM3R171400532::INSTR', 'ASRL1::INSTR', 'ASRL3::INSTR')
Then open the DMM like this:
dmm = rm.open_resource('USB0::0x1AB1::0x09C4::DM3R171400532::INSTR')
You can query the instrument's ID:
dmm.query('*IDN?')
Out[6]: 'Rigol Technologies,DM3058E,DM3R171400532,01.01.00.02.02.00\n'
And measure voltage like so:
dmm.query(":MEASure:VOLTage:DC?")
Out[7]: '1.230074E+01\n'
That's 12.30074 volts.
See the DM3058 Programming Guide for more commands you can send it:
http://www.batronix.com/pdf/Rigol/ProgrammingGuide/DM3058_ProgrammingGuide_EN.pdf