I figure I'll just use the super tiny seramis and maybe some spag or synthic. Hopefully, roots are not too terrible. Flowers smell really nice! :)

Oncidiums can lose all their roots and come back well. The important thing is to put them in something like fine bark, and keep them wet enough.

Update:
I have tried flushing the plant as dollythehun suggested, but I think the media is too far gone.

The flowers drop off easily and the leaves continue to yellow and be lost. I have been keeping an eye on it and making sure the media doesn't dry out completely. I have also noticed that it was potted too deep in the pot which I'm sure is another part of the problem.

I think I will be forced to cut the flower spikes and repot or risk losing the plant. The media just may be too far gone and the ventilation may not be enough. There are holes on the bottom of the pot, but not as many as I am used to. I will probably make more, repot, and hope for the best.

Do you have any pictures of the HD plastic bins and egg crate set up? I'm curious how it worked out

Check out this photo on my website
http://orchidcentral.org/GrowingAreas/indoor.jpg

This is what I did back in the days when I lived in a condo and used the spare bedroom as my "greenhouse".

Startling Discovery
 

More updates:
So I took out all the media to find mostly charcoal and one microscopic piece of sprag. I found not one plant, but 2! One with 5 rotting pseudobulbs in the media!!!:shock: I have NEVER seen a case this bad, where it looks like someone literally shoved a plant under the media and didn't care. It's surprising because I got it from Hausermann's during their open house. The whole thing smelled awful! So I trimmed dead roots, which surprisingly there was not that many of, but I did lose quite a bit trimming off mushy parts. The plant on the right was in really good shape, but I'm not sure the plant on the left will make it. I closed all the wounds off with hydrogen peroxide and repotted in leca and seramis. Mostly because the roots are pretty delicate and I needed something more water retentive.

I'd strongly urge you against ever using hydrogen peroxide on orchids. It is very caustic to them, can eat the velamin right off of roots and cause damage to green tissue. You couldn't do much worse pouring drain cleaner (or hydrochloric acid if you prefer) on your orchids.

Seal cuts with a dab of cinnamon powder.

I do use cinnamon powder too. And hydrogen peroxide was extremely diluted. Probably about 80-90 percent water. But if it is that bad I will stop using it.

Is it still caustic at the stated dilution? I have used even less before. It's the regular 3 percent but super diluted. I usually only use it when there's a major problem. Such as a bunch of mushy pseudobulbs or lots of fungus on roots. Flower spikes and regular wear and tear are sealed with cinnamon. I rinse with water after using hydrogen peroxide, not the cinnamon.

Also wondering why it is caustic (not doubting it, as this is the case for people), when it breaks down into water upon contact with light? Is it just the reaction that makes it so?

At that low dilution it is probably not harming anything, but not doing much, if any, good either. If you want a fungicide in addition to cinnamon (which is quite good for sealing cuts) you could use Physan, which is not harmful to orchids at the dilution recommended on the bottle, and does a decent job.

Physan is what I use. Does a good job.