Problems with wordpress redirects of a site inside a site

I’ve been digging through all sorts of tutorials on this and messing with a bunch of multisite/htaccess stuff. Let me give you my scenario and see if someone can tell me what in the world to do to make it work.

I have a wordpress site in a folder
/mudmin6
That site is mudministry.org

I have another wordpress site (totally separate) in a subfolder of that site
/mudmin6/userspice
That site is userspice.com

Ideally I would like to be able to access this site by typing either of these two things…

mudministry.org/userspice
or
userspice.com

So far, that works. However, I can’t do something that’s really important.

I can’t type, say
userspice.com/forums and get to my forums. I get an internal server error. The only way to get to the forums is to go all the way back to mudministry.org/userspice/forums

Can someone tell me what needs to change in my .htacces, wp-config, or wordpress dashboard to make this happen (and in what subfolder to make these changes?)

.htaccess for mudministry.org

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

<Files 403.shtml>
order allow,deny
allow from all
</Files>

.htaccess for userspice

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /userspice/
RewriteRule ^index.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /userspice/index.php [L]
</IfModule>

# END WordPress

I know that there are a lot of people who will say why do I need to do this? I need to do it for a grant we have. The initial domain must be accessible by mudministry.org/userspice but it’s also really annoying that I can’t type userspice.com/anything and get to any of my pages.