In some ways, you can't. In other ways, you can. Most likely, the mods on the 1.6.4 server aren't compatible with the mods in the Technic Launcher. You could ask the owner of the server to list all of the mods and try to see if they're all in the Technic Launcher. If they are, you could try using the Technic Launcher to play on the 1.6.4 server. This might not work if the pack you're using on the Technic Launcher is 1.7.2. You could try to use an older version, but those may be less stable.
If they aren't compatible, another option would be to locate the Startup folder. Open the start menu, and click on
All Programs, which is at the bottom. Find the folder named
Startup, and right click. Click on the option open. Copy and paste all of the different Launchers you use into the folder. Whenever your computer starts up, all of the launchers will open, so you have easy access to all of the Launchers. However, this method would only work if you restart your computer often.
Another option would be to use shortcuts, but those are boring. To create shortcuts just right click, hover over
send to, and press
Desktop (Create a shortcut).
The more fun way is to use batch files. Batch files run commands for your computer. To make one open a file, you need to first create one. Create a text file, not rich text, just an old Notepad text file. Name it whatever you want. Open it up, and first type start, then the location of your file. then type param1. So, mine would look like this.
start C:\Users\Kids\Desktop\Minecraft.exe param1
This will open my Minecraft launcher, once it's in batch form. Click
Save As, and change the extension on the bottom bar to
.bat. Save, close, and delete the other
.txt. Double clicking on the new file will open whichever file you want.
I hope this helped!