Dynaudio S3.4 vs S5.4

Hello all. I am a newbie as this is my first post, but have participated in the market using Audiogon. Looking for some advice. Am interested in both the Dynaudio S3.4 and S5.4 speakers but am concerned on whether amplification will adequately drive these speakers, as well as concerned about room reflections. Sooooo, I thought I would ask the experts.

Amplifier is a Pass X150.5 (150 into 8 ohms, 300 into 4ohms), I'm currently driving Thiel 1.6s. Room size is 13' wide, 23' long, and 10' ceilings. Dynaudio dealer told me that putting a good 7-8 ft between the speakers is a good rule of thumb (without seeing my setup) but that would leave 3' on each side, as well as 3' behind the speakers. Problem is this is a living room, and treatments are not a realistic option (from a WAF perspective). I'm extremely impressed with this company, and have heard the 5.4s, however they were mono'd using Simaudio amps, and I will not get the opportunity to try my amp with them. Thanks for any feedback you may have.
Given that room treatments are not a possibility, I'd be looking at the S3.4's or C1's with a subwoofer.

I have owned a pair of 5.4's for about three years now, and still love them. My system has improved so much since acquiring them, they just kept sounding better and better as the system grew around them. I first heard the 3.4's, and thought they were the smoothest sweetest speakers I'd ever heard. You can't go wrong with either one. I drive my 5.4's with 300wpc, but recently I had to drive them with 100 watts, as my 2ch. amp was being upgraded. I was surprised at how good they sounded with the smaller amp, so I think you would be happy with your current amp.

You can get by with a little less spacing between the two, and still get good results. You can try the foam plugs in the vent for closer spacing to the walls, if need be.

If you get 'em, you're going to love 'em!

Thanks much for your input. Still unsure on whether to ramp up to the 5.4s or stay with the 3.4s. If wife can deal with the new "gateway" into the living room, I'll probably make a run at the 5.4s. The porting issue is especially helpful to contain room resonances. Thanks again and have a great Christmas.