Thank you for contacting Presonus Technical Support. Sorry to hear about the recent issues you have been experiencing.
The Performance Monitor and windows task manager performance meter are unrelated. The Studio One Performance monitor relates to what is happening in Studio One.
Mai Tai can be heavy on the processor. I don't recommend going over 6 Voices or changing the Quality setting above Normal. You can try lowering the voices and see if that makes a difference.
Also, using an audio interface that has an ASIO driver can help with performance. You can download and install ASIO4all and test to see if this makes a difference. Presonus in no way supports ASIO4all, but I have seen it help in situations where only Windows Audio is present. An ASIO driver provides a low-latency and high fidelity interface between a software application and a computer's sound card.
If the issue remains, please create a ticket to technical support.
Here is a link to create a ticket: http://support.presonus.com/hc/en-us/requests/new