@pooch2 Your current speakers will be a disappointment with an amplifier of only 4-5 Watts.
My speakers at home are 98dB and I like more than just 4-5 Watts on them as well, although most of the time that sort of power would be fine.
If you do change out your speakers in favor of something 10dB more efficient (which will mean that your amp need have 1/10th the power to make the same sound pressure), keep in mind that with SETs whatever power they are rated for is not their ’usable’ power. With SETs you really need to not push them past about 20-25% of full power if you want to hear what they are really about. At power levels above that they will start to sound ’dynamic’ due to the excess distortion they will make at those power levels. All that you’ve read about how ’dynamic’ SETs are is the result of people doing exactly that.
Dynamic contrast comes from the signal, not the amp!
After 30 years of studying SETs I remain unconvinced that they offer anything if musical reproduction is your goal. A push-pull amplifier of the same power stands a very good chance of sounding better in every way. There aren’t that many 5 Watt PP amps out there; I built one several years ago just to verify this fact. The additional bandwidth, lower distortion and greater percentage of usable power in a good PP amplifier makes for smoother sound, greater detail and overall more impact.
For your existing speakers I would recommend something with at least 100 Watts in most rooms. The problem here is that tube amplifier power is expensive and 100 Watts is close to the limit where the power bandwidth of the amplifier can be considered high fidelity. As you increase the tube amplifier power, the output transformer imposes bandwidth limitations (this is particularly true of SETs where above 8 Watts is challenging to be considered ’hifi’). With PP amps this limit is around 100 Watts.
There are tube amps that don’t use output transformers and so bandwidth is not limited by how much power they make. These amps are called OTLs (Output TransformerLess). There are also class D amplifiers made now that sound for all the world like a really good tube amplifier. So you do have some options. Low power is fun, but unless your speakers are really efficient or you’re only playing the system in a bedroom or the like, you’ll run into power limitations.