What's your idea of a large number of files? On my DNS-323 I have a folder that contains in excess of 208,000 (two hundred & eight thousand files) with a total capacity of 21.6GB, so that would be an average, I believe, of 100k.
The DNS-323, in my opinion works just fine with large numbers of small files - I grant you it's no speed demon though.
One caution - the DNS-323 was NOT designed to have it's disks swapped in and out repeatedly - so don't get upset if you lose data as a result of doing this.