Avoiding prompt if no sound card is detected speakup.synth=soft

[john doe <johndoe65534@mail.com>]

Hi,

I'm trying to avoid that below prompt when preseeding with
http://ftp.debian.org/debian/dists/stable/main/installer-amd64/current/images/netboot/gtk/netboot.tar.gz
:

"No sound cart detected after 80 secs
Can not do software speech synthesis
press enter to continue anyway"

How can I preseed that prompt?

What i'm trying to do is to install Debian with accessibility
('speakup.synth=soft') support regardless of if a sound card is detected.

I've tried 'espeakup/card=false' and/or 'espeakup/voice=false' as kernel
boot parameter to no avail.

Any input is appreciated.

--
John Doe