Hi, for budget reasons, I downgraded from Isabella (non-LFP) to Isabellina HPA LFP-V plus Sig 15. So in my current situation, the Sig 15 is acting as an integrated amp and the HPA is the DAC.
My guess is that for those with the budget, the current Isabella LFP-V would be an upgrade for most systems. Add the new ProDac and you will be flying in a very rare hi-fi strata.
As far as the Sig 15, here you are looking at an alternative to your current SET. Will it be better or worse?... only listening would tell. But from my experience, the Sig 15 is an exceptional unit, especially when the tube is upgraded beyond stock.
Kent