I love my Signalink. I mostly use it with AGW (sound card packet) but have
tried other modes.  

There are things you can do to ensure your screen reader never tries to use
the card. (The SignaLink is a USB sound card, and by default, once you plug
it in, the screen reader may try to speak through it, which you do not
want.)
 
For example, This works for JAWS and any sort of secondary sound device you
want to ensure JAWS never uses.

Find the exact name for your primary sound device, or any device you want
JAWS to consistently use. For example, in XP, I go to volume control, and in
its menu, select Options and properties. There is a list of "mixer" devices.
My particular choices are "Sound Max HD Audio" and "Microsoft Sound Mapper",
and since I want the first choice, I use the virtual buffer in JAWS
(Insert-Alt-W) to capture the exact text of that "mixer" name. Note that
some Windows programs, for example Studio Recorder, call it a "Wave device"
but mixer, sound device  and wave device are synonymous Windows terms.

If you use something occasionally, like a Plantronics headset, bluetooth
speaker or Skype USB phone, when it's not connected it doesn't appear in the
list.

In Windows 7, with some generic USB speakers connected, I find the mixer
name by  typing Sound in the search box, and from the results list, I select
"change sound card device". It takes me to control panel's "Sound applet" on
the playback page, where a list of devices is displayed. In my case, I have
a device named "speakers"  and another device called "Speakers, 3-D-Flex". I
had to unplug and plug back in both sets of speakers to figure out which was
which. The 3-D flex were some generic things I picked up at a swap meet
which make JAWS sound awesome and music sound dreadful.
  
Once I've got the exact string with proper spelling,spacing  and
punctuation, I open JFW.ini  or synth.ini.

Go to Jaws, Explore JAWS, Explore program Files, and if it's JAWS 14, you
want synth.ini. If it's an older JAWS, you want jfw.ini.

Inside JFW.ini, find the entry for eloquence:
Synth1Name=eloq
Synth1LongName=Eloquence Software
Synth1Driver=eloq

And below that add:
Synth1Port="Sound Max HD Audio"

.. Or whatever string you discovered is the exact name for your mixer
device. Put it in quotes, with only spaces inside the quotes if spaces are
part of the string. No spaces on that line outside of the quotes. If you
make a mistake, you loose speech -- so be warned! 

On one of my machines, the actual audio device is called "RealTek
High-Definition Audio" but on another, that's simply a comment in the list
of devices, the actual mixer name is "Speakers".

If you use JAWS 14, the synth.ini is a bit different:
[Eloquence Software]
ItemLong="Eloquence Software"
ItemDriver="eloq"
ItemShort="eloq"
ItemType="Driver"
ItemPortString=""

Synth.ini already has an entry under eloquence labeled ItemPortString so you
just put your mixer name inside the quotes. For example:
ItemPortString="Speakers, 3-D-Flex""

Notice that in this last example a comma was actually part of the mixer
device name. Be super careful to get the exact string correctly nestled
between those quotes! Don't mindlessly cut and paste from instructions on
the net!

If you like to use the JAWS voice profiles, you can actually configure
different voices to use different sound devices. In my case, I've got my
laptop set so that no matter what I plug in,JAWS wil always, always use the
built-in speaker.  

It's a very good idea to back up those ini files first, and to have an
alternate screen reader available, such as NVDA if you mess something up and
loose speech, or if my instructions, which work great on my machines, fail
to work on yours. I can use my Braille display to bail me out when speech
goes south, and I've got a sighted hubby who will rescue me if all else
fails, but you might not have these advantages.

Last disclaimer: I'm not a JAWS tech support person; just a hobbyist who
likes hacking JAWS, so there are no guarantees here!

--Debee [KF6BKR]