Studio lighting kit
I agree it is inconvenient, but there are still ways to use studio flashes with the a33/a35/a55; you just need to take some extra (PITA) steps. Here's my understanding of various ways that will work (although I'm sure others are more knowledgeable than I)—all involving the built-in flash (or a flash connected to the mounting shoe). [Assume the built-in flash.]
a) With the built-in flash “engaged,” the a55’s EVF will “gain up” even in manual exposure, allowing you to see your subject when the ambient light is low. If you are using the built-in flash as the remote trigger for the studio flashes, and if you don’t mind the direct light coming from the built-in flash, you are done!
b) If you mind the light in your pictures from the built-in flash, but want to use it as the remote trigger for the studio lights, it is my understanding (I've never tried it) that you can essentially let the infrared light through but block the visible light, by putting (in make-shift fashion) a piece of exposed film in front of the built-in flash’s light.
c) If you want to connect the studio flashes directly to the a55, and don’t want the light from the built-in flash to “contribute” to your picture, then you need to (a) tape over (with opaque tape--or otherwise block) the light from the built-in flash and (b) attach to the mounting shoe a small adaptor that contains a standard flash socket (since the a55’s body doesn’t have a standard flash socket) into which you can plug a studio flash.
d) If you want to use remote radio triggers, follow (a) from the prior paragraph and (b) attach the remote radio trigger to the remote socket on the a55.
All of these methods use the built-in flash to “gain up” the EVF, keeping it from going black. The trick becomes if (as is common) you don’t want the built-in flash to contribute to the lighting.