Cases for the Garmin GPSMap 76CSx include:

Thin film screen protectors such as are commonly used on portable MP3 players and and PDAs work well on the unit.

You may either cut a commodity screen protector to fit your Garmin GPSMap 76CSx or use a precut screen protector like those from Nushield and Strong Engineering, or Invisible Sheild.

The expandable memory in Garmin GPSMap 76CSx is used for storing detailed maps, custom POIs, and tracks.

The Garmin GPSMap 76CSx uses MicroSD memory cards, a type of memory developed largely by Sandisk in 2005 and commonly used in cell phones. It was formerly known as Transflash. It is electrically similar to Secure Digital (SD) but it is not physically compatible. Most MicroSD cards come with an adapter that let them be used in SD readers and writers.

Garmin does specifically recommend against using the popular SanDisk Ultra II 1 Gb cards.

When the products were launched in Jan 2006, 512MB was the largest available on the market, so the manuals and Garmin's web site answered this question with "512MB". You can still find references with that outdated answer.

1GB and 2GB MicroSD cards becamse available later in 2006. They work fine. Garmin specifially warns against the SanDisk Ultra II 1 Gb.

In 2007, 4GB and 6GB microSDHC cards became available. However, the units remain bound by a 2GB limit for a single map file in most mapping products. That's not terrible; 2GB holds the entire U.S. for any Mapsource product. The GPSes are limited to 2025 map tiles and the Topo product, in particular, uses tiny (county sized) tiles so it's easy to run into that limit long before you run into the 2GB limit.

City Navigator Europe v9 (NT-not) has been confirmed to support maps > 2GB and it appears that the 2GB limit still holds true if multiple mapping products are used.

In March, 2009 firmware version 3.90 (the number varies a little from model to model) added support for maps greater than 2GB, but the 2025 segment limit remains.

Yes. MicroSDHC support was added in the firmware around March of 2007. Still, there are excuses.

MicroSD cards of 4GB and 6GB have been confirmed to work in the Garmins with MicroSD sockets. The limit of 2025 segments or 2GB, whichever comes first, still comes into play. The remaining space can be used for tracks, additional track storage, or for storing non-Garmin data. (Note that 6GB cards were a relatively short-lived product in 2007 or so and have faded to obscurity.)

The exact limits seem to be hard to pin down and building and transferring large datasets for experimentation is time-consuming. As a practical matter, the Topo product seems to be the only one to run into the 2025 segment limit and most continents for the other products take under 2GB.

Cards of 8GB have been confirmed to work, but since these devices can only handle a single gpsmapsupp.img file which is limited to 4GB and that provides no way to switch between them, there's little incentive use a card larger than 8GB. An 8GB card will hold the largest maps addressible by the unit and have plenty of space for tracks.

No. The speed matters in write-dominated devices like cameras. The Garmin GPSMap 76CSx mostly reads from the MicroSD. There is no perceivable difference in the speed of the MicroSD you install.

Yes, the Garmin GPSMap 76CSx supports use of an external antenna.

Garmin eTrex Legend Cx™, Garmin eTrex Venture Cx™, and Garmin eTrex Vista Cx™ do not support the use of an external antenna.

Garmin 60Cx™, Garmin 60CSx™, Garmin 76Cx™, and GarminG 76CSx™ can support any external antenna with a Micro CX (MCX) connector such as: