Watchguard Firebox and PowerConnect 3324

Hello,

I purchased a Watchguard Firebox x500 through Dell a few weeks ago along with a 8 port unmanaged switch.  I flew out to Colorado where my servers are located and installed the hardware.  I used "drop-in" mode on the firewall configuration as I have sufficient IP addresses.  Each server has two NIC's.  I plugged the two NIC's from the two servers (PowerEdge 2550's) into the 8 port switch, the switch to the Trusted port on the firewall, and then the data center's external to the external port on the firewall.  To make a long story short, I was never able to get that configuration to work so I had to go to x-over cables, one from each server, one to the trusted, one to the optional, and all has been running fine.

I decided to try something new and purchased a Managed Switch for other reasons as well, and installed it this past Thursday.  Same configuration as previously attempted, two servers, connected to ports 1-4, port 24 to the Trusted of the Firewall, then Firewall out to the Internet via it's External port. Some IP's/Sites would work, some not.  I couldn't use the IP address set to the switch either to access the GUI from the outside, but could from the remote desktop to the servers via their web browsers.  After two days of terrible/intermittent service to my hosting clients, and 3-4 hours on the phone with Dell confirming the switch is configured correctly, which was done twice with them on the phone, we finally pulled the plug on the Firebox and plugged external to the switch and all worked fine. 

I went through everything from using Auto-Negotiate to hard set 100M-Full Duplex.  Still the same.  It was odd as at times I'd see 100M-Half when in Auto mode.  The cables are fine, they were replaced in troubleshooting, and there are no errors showing on the switch.

The question is, how to make the Watchguard Firebox x500 and the Managed Switch play well with each other.  Has anyone else experienced issues such as this that would steer me to getting this resolved?

Thanks!