the MAX233 is a physically larger (longer) chip than the DS275, so it won't fit in small places [its a 20 pin chip from memory, so thats 2.5 times longer than a DS275].

But, the Oncore suggested design for power & MAX233 chip is perfectly simple to make as well.

You only need 4 wires from that circuit to run the GPS.

2: 1 for power and 1 for Ground and two more for Serial In & Out [called TxD and RxD usually].

The Gound on the Serial port (pin 5 on a DB9 connector) is shared with the "Ground" on the PT5101 and The ground on the MAX233 chip.

You simply wire the 4 wires from your "black box" circuit with the MAX233, PT5101 and 1 capacitor in it, to the GPS [you will need a small (not .1 inch spacing)connector block to connect these wires to your Motorola GPs - your best source is to probably visit a electronics junk shop and buy an old dot matrix or laser printer and scavenge the block connector out of a piece of junk like that (they tend to use them to link the fonrt panel to the printers main electronics) than to try and make your own from scratch. You can cut down a larger connector (with more 'pins' in it than you need, not a connector thats too large) to the 10 or so pin connector block that the Motorola wants with an Xacto or similar knife. You can usually remove the pins from these block connectors with a very small screwdriver or a small point [like a needle or pin etc] - lift the small plastic 'lock' on the side of the connector block up, and then the pin slides out of the block.
You only need to populate the connector block with the 4 actual pins that the Motorlola needs to operate.

If you want "battery backup" for the GPS, then you can add 2 more wires for the battery backup and wire that up to a small 3V or whatever cell - making sure it can't short out when its in the car! But thats not necessary - the GPS will work without it, but it will take a bit longer to get a lock from when the car is started.

Then you Route another 4 wires from the (DB9 Male) Serial connector the the
"black box". You need 2 wires for TxD and RxD signals that go to the RS232 output and input on the MAX233, 1 ground wire, and the +12V power wire that goes to the +12V the Empeg outputs (on pin 4) of the Docking sled serial connector [or elsewhere in your car - such as the accessory line, where its only powered on when the car is - otherwise you'll flatten your car battery evenutally if you leave it permanently wired into your cars battery].

Thats it, easy to build, and you'll have you Empeg hooked up to your GPS in no time.