I posted something similar a year ago--
We have three bio kids, and the two oldest are twins with pretty severe developmental delays (they have seizures, cognitive delays, physical delays, and are non-verbal). We were worried that we might get turned away by international agencies.
We first pursued an adoption in China through the Great Wall agency. They were very, very helpful. They can talk about your specific situation with the CCAA (Chinese adoption authorities) before you put any money down... they can't give 100% assurances, but they can give you a pretty good idea of whether you'll be accepted or not. In the end, we couldn't go with China because we didn't make enough money (10K per person in the family).
We then looked to Korea. We found an agency in Michigan that works with out-of-state couples. The nice thing about this agency is it's the US-based social workers that match babies to families, so it's very easy for a person that knows your family (your social worker) to have a clear idea if you'll be able to parent a baby while having other special needs kids. In this case, it's your social worker (the person conducting your homestudy) that makes the decision if you'll be a good adoptive family or not--and that's nice, because then you don't need to worry about some international office on the other side of the world saying "NO" just because they see you have special needs kids.
Our homestudy was a little different, possibly, than the homestudy of a more typical family. We had to get a letter from the boys' special ed teacher about how we are as a family (in terms of supporting kids with special needs). Where we talked about Ian and James' special needs the most was in our homestudy autobiographies--about how their special needs have changed our lives, and changed us as parents. Honestly, the social worker didn't even blink at the thought of placing a baby with a family that had two special needs kiddos...I think (like previous posters mentioned) she sees it as making us stronger, better parents. It's important to be upfront and open about your child's disabilities and how it's changed you as a family, and it's important to have life insurance and will, and they will want to know you've discussed guardianship and financial resources for the future--but you don't have to show that you're "perfectly" prepared or anything. We also wanted to show the SW that, just because our boys are disabled, that doesn't prevent us from getting out and about with them. We were very sure to talk about how active we are as a family, and how we make very special efforts at doing fun things as a family.
Another place where our boys' needs came up was in the homestudy session where we talked about our marriage and our relationship... we talked about how families with special needs kids have higher divorce rates, and how we're being proactive about keeping our marriage strong despite the stresses. We were very open with her about going for marriage therapy, and about what we've worked on in therapy, and about how we work with the stress. (That being said, it's important to realize that you're working to portray yourself in an honest, but GOOD way...you can talk about therapy, but the homestudy isn't a therapy session, if you know what I mean.)
PM me if you have any questions, or if I can be of any help. I think, in most programs, being the parents of a kiddo with special needs will probably reflect very well on you as parents. It might help if you can find an agency that does the placement matching here in the US, rather than overseas, but even that isn't really necessary. Remember--a lot of adoptive parents adopt multiple special needs children, or some special needs and some typically developing children--so agencies are used to seeing families with kids that have special needs.
Good luck! This has been a great, positive experience for our family so far--I hope it is for yours, too!