Which amp with Wilson watt puppy 8

Your issue is synergy.
There are two main challenges with Wilsons. 
1. they require very high quality amplification and upstream components including cables

2. they’re very sensitive to room acoustics and placement 

when the speakers sound tipped up in the treble this usually means you lack power to drive them sufficiently. It will be more apparent with the Watt/Puppy that used the metal dome tweeter.
To solve this problem you should try 

1. high quality amplifier - i.e. Pass Labs Int-250 if you like integrated amps or X250.5 or X260.8 with either Pass Labs preamp or a tube preamp such as Audio Research Ref5 or Ref6

2. Treat first reflection points (space on a side walls between listening chair and speakers)

3. Treat corners with bass traps. Contrary to the name bass traps improve bass if implemented properly 

4. rug on the floor between speakers and chair

5. good interconnects and speaker cables (no silver)

I don’t know what you use for source components but garbage in garbage out with Wilsons. 

I used Pass Labs separates to drive my Wilson Sabrina, as well as Coda CSiB integrated and now use Boulder 866 integrated amp. You need to keep everything on the level. Wilsons are amazing speakers. You can get a lot of enjoyment out of those Watt Puppies. 
 

Take a look at my system page you can see the room treatments - I use GIK Acoustics. 
https://www.audiogon.com/systems/12098

OP one other thing I wanted to mention is that an underpowered amplifier is more likely to damage your speakers, especially tweeters, than an amp that’s too powerful. So I’d be careful if I were you while continuing to use that amplifier. 

@lendivf good dac. You just need a good amplifier. 
I’m confused about playing over 40% volume. The volume level on the control unit is not an indication of anything. How much volume range you have depends on the amplifier gain and sensitivity. In example on my boulder 866 I usually listen volume at 57 for normal slightly higher than background levels and at 70-77 when I really want to hear what it’s capable of. The 70 level is usually going to get me to around 80db. Max is 100 steps in the volume control. 
My pass separates sounded about as loud with 65-70 in volume. 
 

It’s good to have a large range. 
 

Get good amp and room treatments you should be fine. 

XA-100 are pretty old. See if you can find XA-60.8 or X250.8 and even X350.8. You can drive the amps directly with ps audio dac. Should be ok. 

My Boulder 866 comes out of mute when it’s out of standby at 33 out of 100 on volume scale. You can barely hear anything. Listening at volume 60 is absolutely normal. Pass labs gear is very similar in thar you end up listening at volume 50 and up. I used Audio research Ref6 preamp with Pass X260.8 and going beyond 15 on volume was loud and that’s due to ARC having higher gain. So as I said earlier each amp and preamp is different. You can’t say going above 40 signifies a problem. Also, when I had the PS Audio DSD MkI DAC going into preamp using balanced cables I found that it was noisy if set to 100 or preamp bypass on DAC. At 97 on DSD DAC it sounded the best. 
OP - a typical starting point for speaker placement is 8-9ft apart and about 3ft ftom the wall behind them with the rear ported Wilsons. Toe in almost direct to your shoulders when you’re sitting in the chair again about 8-9ft from each speaker in a triangle. And with Wilsons as I mentioned before you need to treat side walls first reflection points and have bass traps. You just can’t have bare walls and floor. You will get the sound you’re describing. 

@ozzy +1