I have a MOTU 424/2408 MK3 interface in my DAW that is still working well after many years.  All of the analog inputs are being used, and I am considering adding more inputs.
 
Despite the MOTU 424 system being a bit long in the tooth, it seems to be working well for me - in a modern system it seems to handle very low latencies without much trouble. 
 
Another potential advantage is the 424's ability to connect more than one interface via AudioWire.  Since these products are no longer current, one can pick up used interfaces for much less than they cost when new.
 
I've been looking at the HD192, and was wondering if anyone had any experience with them.  I am attracted to them for the big I/O metering, and it seems like with would be a plug and play addition to my system.
 
Does anyone know how the A/D converters are in this interface?  Are they superior to the ones in the 2408 MK3?
 
If you have anything to share to recommend or warn about this interface, it would be most welcome.

The HD192 apparently is a discontinued unit, but if it is a perfect match to your working system and you can still get it, then you probably should ... there are a few on ebay at a reasonable price ...
 
Before spending the money I would still have a look at the new AVB series (up to date drivers, lower noise floor preamps, and perfect scalability, ...) to double check whether the HD192 is indeed what you need.

Yes the HD192 discontinued, so there is some risk of being orphaned. 
 
The AVB series does look awesome, but I could get a used HD192 for 1/3 (or less!) of the price. 
 
I use external preamps, but am curious if the HD192 converters are anything of note.  If they are, it could be a bargain upgrade.

The HD192 converters are superior to those in 2408mkIII.
IIRC, The HD192 uses the same converters that Avid was using in their 8-channel ProTools Interface (of that time).
 
You won't find a better low latency performer than the MOTU PCIe 424.
Though the system is long-in-the-tooth, you won't be disappointed.
 

Thanks for your reply.  It seems that there are HD192's out there for 3-5 hundo.  While there's some risk, it seems to me that's a good price for 12 nice converters.