You could also consider up-sampling your project to 96kHz and working with the libraries you have. Seems like a petty to build a new preset collection just for one project, and your 88.2kHz Nebula options are quite limited. I've done a lot of 44.1k/48khz to 96k up-sampling (in order to use my 96k presets) and I prefer that over Nebula's own src (multiplied per presets used).
I think it's best if you can stick to the same sample rate in Nebula if you can. I must say that I much prefer the sound of this rather than SRC down in Nebula.
Like Yr says, If you can't find the correct sample rate presets for your project and you are going to use many that are converted down it may actually be better to not do that and SRC your project first.
For best results your best to keep your project clean all the way through , strange artifacts build in no time.
The main reason I create 88.2 and 48khz is for my own projects, after many tests I started using these sample rates.. In the process I came up with my own sampling techniques to improve transparency. This was not a over night set of techniques I came up with but came over months of experimentation and it benefits you guys having those extra native sample rates. for me the sweet spot is at those sample rates, 44.1 and 96khz I create because it's a standard here and also It will get me out of trouble If I'm forced to work in any sample rate .
My first release was not using all the techniques I use now and was pretty much a standard way of sampling but originally kept that release to 88.2 because that was the rate sounded best for me at that time....