Y cords would work but you may run into hum problems if you are going into two different guitar amplifiers as they maybe at different ground potentials. A better way would be with a transformer that has an input impedence of 50K ohms and two outputs of 50K ohms. An old interstage driver transformer for a push pull output stage from a tube amplifier would probably fill the bill. Look on the WWW. The other way would be to use a direct box with a y connector on the output of the direct box. Problem is it would also drop the signal down to microphone level which may or may not be what you are looking for.

Hope this helps.

forget about Y-cables, a splitting box is unavoidable.
i can tell you by experience it's either saving money or saving problems. try before buy and be sure there is no hum or essential loss of sound quality.