> 1) Yes.  Try the Leased-line mode

This is a four wire hookup, and it does not change the output circuitry.
If it needed current, then it would still need current.

> 2) Would not do that (putting 30 volts on the line).  First try without
any
> voltage. After that try a voltage of about 9 to 16 volts (Educated guess
> :-) thru a protection-resistor af about 330 - 680 Ohm (current thru either
> of the Modems should not exeede 15 mAmp).

The minimum telco current in the US is 20mA. The circuit may not function
below that level.

The proper circuit is a series connection of the two modems, and a current
source which is bypassed to allow the AC signal to pass, as I described
previously.