No 4dB signal loss. You haven't "transformed" or electronically changed the signal, except for putting more connections and more cable between the source and destination.
I'm guessing you have the snake in the loud room, and are connecting mics in there, then you want it coming into the control room...but you want it to go to a patchbay with 1/4" TRS connections, then out of that into the mixer?
What makes me wonder, though, is your use of the word "converters". If they are just XLR-1/4" solid, or perhaps short patch, converters with no electronics other than connector-to-connector wiring, the same as above is true. Keep in mind that it MAY be better to use adapters with a short length of cable for one reason. If you have an XLR socket connected to one of the solid metal adapters sticking straight out of a 1/4" jack on the vertical back of a mixer...that may be a lot of weight for that jack socket. If you have a 1/4" plug sticking out, with a cable that dangles down, and THEN connects the XLR, it's not quite so much stress for that socket. Yes...it's not MUCH more or les, but anything that lessens any amount on the jack socket is good.
If you are talking about some of those XLR-1/4" impedence converters...than something will change.
If you wire your patchbay properly, you should be able to connect the LA610 inputs and outputs to it, and then use it on whatever channel you want by simply patching it into the path with patch cables...that's what patchbays are for. In other words...you don't NEED it connected to channel 9. Leave it in it's own little world, and patch in whenever you want.
The connections on my audio computer's rack mount I/O are on the back, so I use a patchbay for convenience. But, I can patch into the path anything I want....pre-amps, effects, whatever.
Perhaps clarify your term "converter" for a more definite answer? I realize it does kind of convert one connection type to another, but converters in the audio world are generally things that convert an electrical (or data) signal. Adapter is the more commonly used term for things that adapt one connector type to another, and I suspect that's what you are referring to?
The only reason to use a patchbay in your scenario is if you sometimes want to interrupt the input path to one of the mixer channels at some point. With the pre-amp, you may want to do that. Or, you may want to have a guy sit in the control room and record bass direct...whatever. Otherwise, you really don't need it. You are just adding more potential points of signal loss and noise introduction that you may have to track down later.
(Edit: I don't even know if the LA610 provides phantom power...so some of the next stuff may, or may, not apply. Also, apparently it has XLR and "Instrument" inputs. You may investigate how you will work all that into this).
If ALL you want to do is to sometimes use the pre-amp on a track, you may consider the possibility of moving the pre-amp to the source end of the snake, if possible. If the pre-amp is used to power a condenser mic, you probably want that plugged directly into the mic, anyway...instead of backing through a patchbay, through a couple of adapters, and 50 feet of cable. You really want the fewest points of possible electrical disruption with that. If a connection fails AFTER the pre-amp, fine. If it fails between the pre-amp and mic....mmmmmay cause a problem. That way you can easily and quickly just plug it in between a mic and the snake on any channel. I realize this takes the control knobs away from the guy in the control room, but if it's handy to reach for whoever is singing/playing through it, you can communicate to have them set the proper levels. It also may have the advantage of pushing a more robust signal through the length of the snake, instead of pulling a (admittedly not much) weaker signal through.
That way, if you connect the tail ends of your snake directly to the mixer, you have eliminated potential failure and noise points.
There may be other uses for the patchbay, if you have more outboard equipment, though.
Don't use it just because you have it. Use it because you NEED it. And, you MAY need it, if you really want to keep the pre-amp in the control room. It's your call. I'm just throwing stuff at the wall (as usual) and letting you scrape off what you want :shock:
Hope this helped