There is a whole class of these, and attestion of comparatives can be hard to find, but my feeling is these are all -chaí in Munster. Look at these:

atruach, atruaiche (atruachaí?)
buíoch, buíche (baoch, baochaí?)
diomách, diomáiche (diomáchaí?)
lách, láiche (láchaí?)
neamhspleách, neamhspleáiche (neamhspleáchaí)

The only evidence I have is that Séadna has "ar an bhfear is saidhbhre agus is neamh-spleághchaíghe i n-Éirinn". I seem to be generalising in my mind to all the others, based on the hunch from this sentence.

Ó Sé gives baothúla and baothaí as the comparative of baoch (buíoch) (section 322/323) and láithí for lách.

I would need to look into it more closely but I think what you say above is correct.

You are probably already aware of this but from the bit I know the -iche endings are used in Conamara in the comparative

Are yes, the -iche must be from the Conamara.

Carmanach, what you are saying is that there is some doubt if these endings are /hi:/ or /xi:/, right?

quote:

Carmanach, what you are saying is that there is some doubt if these endings are /hi:/ or /xi:/, right?

No, I'm saying that I'm almost sure they're all /hi:/. To me, /xi:/ would sound strange. Ó Sé has a reference to it somewhere but I haven't got time at the moment to go look.