Yes, there are digital-to-analog converters (DACs) with an 8V analog output range and serial input interface. One suitable example is the Texas Instruments DAC8551, which features a 16-bit DAC, SPI serial interface, and can accept supply voltages up to 18V (allowing for an output range up to 8V). The DAC8551 comes in a small 8-pin package and has good accuracy and low-power operation, making it suitable for a wide range of applications.

You can customize the output range by using an appropriate reference voltage and external circuitry. Please review the datasheet of the DAC for detailed information on configuring the output range and proper use of the device.

the power rails only go up to 5.5V

I apologize for the oversight. In that case, you can consider using the Maxim Integrated MAX5719 which features a 20-bit DAC and SPI serial interface. The MAX5719 works with a power supply voltage of 2.7V to 5.5V and includes an internal 2.5V reference. To achieve the required 8V output range, you will need to use an external operational amplifier (op-amp) in a non-inverting configuration with a gain of 3.2 (e.g., the Analog Devices ADA4665-2). This setup will scale the DAC output from 0-2.5V to 0-8V.

Here's a summary of how to set up the circuit: