The 830MB RAM limit has been removed since long. The default version of the Debian gnumach package will limit themselves to 3 GiB of memory. If you want more, you can try the PAE version, but this requires using rumpdisk for accessing disks.

Note that by architecture design, 32bit systems can only provide at most 4GiB addressing space for processes. With a 32bit kernel, part of is is used by the kernel. It is also possible you use a 32-on-64 kernel, to provide the full 4GB adress space to userland. To give more to userland, use a fully-64b Hurd.