Tell me more about the sounds
This is a very good question, I suppose also hard to objectively qualify as sound is surely subjective in what sounds good to one person may not be the preference of another.
I’m not sure which exhaust system you currently have but I replaced my Janspeed (OE) exhaust with a 2ubular system. Now it does sound good, perhaps a little deeper and likely a little freer flowing (my guess) but I must admit I do miss that ‘hornets nest’ zing higher up the rev range that it used to have with the Janspeed. How that sound was created I’d love to know.
Video clips of different systems may help though really you’ve got hear them right in front of you.
Good luck!
I used to run a Larini exhaust and that was very nice…
The Elise parts (Tullet) system is very quiet, which I like. No issues on low noise tracks like Bedford where I prefer to give the s1 gentle exercise.
I don’t think they supply them anymore.
I have an Eliseparts system and very happy with it, however they don’t seem to list it any longer.
I bought it instead of my originally-intended 2Bular as that never materialised…
I followed a friend’s S1 for many miles and always thought I was being shot at by the local farmer. Bloody loved it… it was an Edwards exhaust and I dunno if Martin had it made locally or something but definitely sounded the business and not just in a silly pop-bang way.
I’ve got a Larini exhaust and it sounds decent, but quieter than the OEM Janspeed oval. I would say that the Larini and decat’d is noticeably quieter than the Janspeed with a cat!
Definitely Larini
Doesn’t matter, all S1’s sound epic 
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hi folks - orignal mild steel Janspeed without a cat IMHO - Stainless steel systems sound to " tinny " to my ears they sound a bit fart box . Ask Janspeed they might be able to help. Its not just the exhaust , its having a nicely tuned engine K series for that grumpy start to screaming 8 k soundtrack 
hope this helps you albeit late . Sound demo any time please contact me . - Dave