I've gone through the server or nas options pretty thoroughly now. Conclusion for me is that a server has more possibilities than a nas. Basically because anything that can be run on Linux can also be run on a server even remotely controlled if needed. Things aren't so simple on the nas software I have looked at which probably comes down to their original aim - just to serve files. There are many add ons for self build and also hacks to commercial nas's but it looks like building up a box complete with one of the low overhead desktops and adding the required software is a better option if people want to do more with it. This includes less obvious things such as using the boxes own external ports even for streaming video to the telly and other ports for backups. The desk top on it can easily be remotely controlled. I'm not too keen on working in the console unless there is no other option.
As far as ZFS file systems go which initially attracted me mdadm raids can be scrubbed periodically to correct errors which to me is more or less the same as the self healing ZFS offers. For some it's a pity that mdadm doesn't offer Raid 0 with parity partitions allowing them to be scrubbed as well. If it did I suspect my box would just have 2 rather large disks in it allowing them to run cooler and consume less juice.
as it is I'm stuck with 4 wd reds.
On the earlier comment about samba why? Turns out that d-link who make there source available do use samba but only reveal as much as they need - user rights, directories, cifs and nfs etc. The latter is an option. Discouraged at the consumer end due to loading. They also make user set up some what easier to understand than the usual samba interfaces. I thought this was the case on most nas's so questioned convert to samba hacks on some sites as samba is already there.